Access time
1. The average time interval between a storage peripheral (usually a disk drive or semiconductor memory) receiving a request to read or write a certain location and returning the value read or completing the write.

2. A measurement of time in nanoseconds (ns) used to indicate the speed of memory. Access time is a cycle that begins the moment the CPU sends a request to memory and ends the moment the CPU receives the data it requested. Memory modules complete this process in as fast as 6ns for PC-133 MHz memory, while older modules can take up to 80ns or more.

Ambyx test system
Also called 'Ambyx Oven.' A burn-in and test system, developed by Micron, that performs burn-in and many functional tests under high-stress conditions to ensure long-term quality and reliability of parts.

A machine that measures critical dimensions of designated areas on the die at different process levels through the use of a SEM (Scanning Electron Microscope).

Application specific processor
Highly integrated logic chip designed for specific applications to work alongside a microprocessor (e.g., a math co-processor, graphics processor, artificial intelligence processor, LAN processor, digital signal processor). These chips offload some of the specialized number crunching from the MPU.

The area of the RAM that stores the bits. The array consists of rows and columns, with a cell at each intersection that can store a bit. The large rectangular section in the center of the die where the memory is stored.

(American Standard Code for Information Interchange) A method of encoding text as binary values. The ASCII system requires nearly 256 combinations of 8-bit binary numbers to support every possible keystroke from the keyboard.

A process in a multitasking system whose execution can proceed independently, "in the background.

Asynchronous Cache
Describes a type of L2 cache that is not in synch with the system clock. Asynchronous cache is slower than its synchronous counterpart, but is capable of delivering information to the CPU at a rate 10 percent faster than standard DRAM. Asynchronous cache was first used to boost memory performance in 386 systems and is still widely used today.

Auto precharge
A Synchronous DRAM feature that allows the memory chip's circuitry to close a page automatically at the end of a burst.

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The capacity to move data on an electronic line such as a bus or a channel. In short, the amount of data moved relative to a specific time frame. It is expressed in bits, bytes, or Hertz (cycles) per second. Essentially, a measure of the capacity of data that can be moved between two points in a given period of time.

A slot or group of slots that must be populated with modules of like capacity and fulfill the data width requirement of the CPU.

Bank Schema
A method of diagramming memory configurations. The bank schema system consists of rows and columns that represent memory sockets on a system: rows indicate independent sockets and columns represent banks of sockets.

Bare board
A printed circuit board (PCB) that does not have any components on it.

Burst EDO - A variant on EDO DRAM in which read or write cycles are batched in bursts of four. Burst EDO bus speeds will range from 40MHz to 66MHz, well above the 33MHz bus speeds that can be accomplished using Fast Page Mode or EDO DRAM.

Ball Grid Array - a square package with solder balls on the underside for mounting. Use of BGA allows die package size to be reduced by allowing more surface area for attachment. Smaller packaging allows more components to be mounted on a module making greater densities available. The smaller package improves heat dissipation improving performance. See CSP and FBGA.

A method of encoding numbers as a series of bits. The binary number system, also referred to as base 2, uses combinations of only two digits - 1 and 0.

Basic Input Output System - often referred to as CMOS, the BIOS provides an interface for a computer's hardware and software. The BIOS configuration determines how your hardware is accessed.

Short for Binary Digit, the smallest unit of data that can be processed or stored by a computer. A bit can have a value of either 1 or 0. Bits make up 'computer' language the same way letters of an alphabet make up human languages. Different combinations of different bits form 'words' and 'sentences' (actually signals) that a computer understands. Before these words and sentences can be transmitted from the CPU to memory, or vice versa, they must be broken down into 8-bit segments called bytes. Older computers were designed to handle only 8-bit data segments, while newer models have progressed to 64-bit segments. This larger bit width capacity generally means better and faster computer performance.

A physical unit of information in a logical record; block size is usually expressed in bytes.

Block diagram
A circuit or system drawing concerned with major functions and interconnections between functions.

Bond pad
Square metallic pads on the die where the ball bond is attached. The bond pad is used to find acceptable eye points.

Buffered memory
This is when there is so much memory the chipset needs assistance to deal with the large loading introduced by the large amounts of memory. A buffer isolates the memory from the controller to minimize the load the chipset sees. This means adding logic, particularly drivers, to a SIMM or DIMM to increase the output current. Buffering is used to overcome signal attenuation due to capacitive loading. Modules that are "buffered" usually have small buffer chips mounted on them.

The process of exercising an integrated circuit at elevated voltage and temperature. This process accelerates failure normally seen as "infant mortality" in a chip. (Those chips that would fail early during actual usage will fail during burn-in. Those that pass have a life expectancy much greater than that required for normal usage.)

Burst Mode
Bursting is a rapid data-transfer technique that automatically generates a block of data (a series of consecutive addresses) every time the processor requests a single address. The assumption is that the next data-address the processor will request will be sequential to the previous one. Bursting can be applied both to read operations (from memory) and write operations (to memory).

The central communication avenue in a PCs system board. It normally consists of a set of parallel wires or signal traces that connect the CPU, the memory, all input/output devices, and peripherals and allows data to be transferred from one system component to another. Busses come in a variety of bit widths and speeds. To prevent data bottlenecks, the components attached to a bus must operate at close to the same speed as the bus.

Bus cycle
A single transaction occurring between the system memory and the CPU.

A unit of information made up of 8 bits. The byte is the fundamental unit of computer processing; almost all aspects of a computer's performance and specifications are measured in bytes or multiples of bytes such as kilobytes (~1,000 bytes) or megabytes (~1 million bytes), or gigabytes (~ 1 billion bytes)

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A small fast area memory holding recently accessed data, designed to speed up subsequent access to the same data. Typically used between a processor and main memory.

Cache Controller
The circuit in control of the interface between the CPU, cache and DRAM (main memory).

Cache memory
Cache RAM is high-speed memory (usually SRAM) which is dedicated to storing frequently requested data. If the CPU needs data, it will check in the high-speed cache memory first before looking in the slower main memory. Cache memory may be three to five times faster than system DRAM. Most computers have two separate memory caches; L1 cache, located on the CPU, and L2 cache, located between the CPU and DRAM. L1 cache is faster than L2, and is the first place the CPU looks for its data. If data is not found in L1 cache, the search continues with the L2 cache, and then on to DRAM.

The property of a circuit element that allows it store an electrical charge.

Card Memory
A type of memory typically used in laptop and notebook computers. Credit card memory features a small for factor and is named for its similarity to the size of credit card.

(Column Address Select/or Strobe)--A control pin on a DRAM used to and activate a column address. The column selected on a DRAM is determined by the data present at the address pins when CAS becomes active.

CAS-RAS (CBR) (CAS before RAS)
CAS before RAS. Column Address Strobe Before Row Address Strobe. A fast refresh technique in which the DRAM keeps track of the next row it needs to refresh, thus simplifying what a system would have to do to refresh the part.

Catastrophic failure
When a device that was initially good now fails to function under any condition.

Check Bits
Extra data bits provided by a DRAM module to support ECC function. For a 4-byte bus, 7 or 8 check bits are needed to implement ECC, resulting in a total bus width of 39 or 40 bits. On an 8-byte bus, 8 additional bits are required, resulting in a bus width of 72 bits.

A detail test pattern designed to exercise each individual cell in the memory and find possible shorts between adjacent columns and data buses

Complementary High-density Metal Oxide Semiconductor.

Complex Instruction Set Computing. This design logic is usually associated with microprocessors. CISC chips use instructions, or commands, that involve several steps in one.

Clock Rate
The number of pulses emitted from a computer's clock in one second; it determines the rate at which logical or arithmetic gating is performed in a synchronous computer. An electrical current that alternates between high and low voltages. The speed of the clock is measured in Megahertz (MHz).

Clock Speed

The rate at which a computer's internal system clock operates. The clock is used to synchronize operations between the components within the clock.

Complementary Metal Oxide Semiconductor. A process that uses both N- and P-channel devices in a complimentary fashion to achieve small geometries and low power consumption. On a PC CMOS generally refers to the BIOS information stored on a CMOS chip.

Cache On A Stick. Coast modules were used to upgrade a motherboard's L2 cache and Tag memory on some socket 7 and older motherboards.

Chip On Board. A system in which semiconductor dice are mounted directly on a PC board and connected with bonded wires or solder bumps. The dice are usually mechanically protected with epoxy.

Part of the memory array. A bit can be stored where a column and a row intersect.

Compact Flash Memory
A fast, postage stamp size RAM that is removable. The CF Card weighs half an ounce, with roughly one-fourth the volume and one-half the thickness of a PCMCIA Type II Card. The CF Card fits into a CF PC Card Adapter making it compatible with a standard PCMCIA Type II slot on any notebook or desktop computer. This allows the easy transfer of stored digital information from the CF Card to a computer or printer. Currently, the most readily available application for the CompactFlash Card is the digital still camera.

One of the major units in a computer that interprets and carries out the instructions in a program.

With respect to semi-conductor packages, the condition of leads in a package having all elements, or all elements in a seating plane, between two parallel planes.

(Central Processing Unit)--The chip in a computer that has primary responsibility for interpreting commands and running programs. The CPU is the most vital component of a computer system. The speed of the CPU has a significant impact on overall system performance, but the CPU doesn't act alone. If slower memory is paired with a fast processor, the processor will be forced to wait for the memory to respond. When the speed mismatch is extreme, the user will see numerous memory errors and even complete system failure.

Continuity RIMMs are used to fill all unused RIMM sockets in a system. CRIMMs do not use any active components, and are used to continue the channel so that the signal can be properly terminated at the motherboard.

Chip Scale Package. CSP is a type of BGA in which the package is roughly the size of the die. CSP is also known as mBGA or micro-BGA.

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In resonant circuits, the decay of oscillations due to the resistance in the circuit.

Data out
The signal line that carries the data read from the RAM (Random Access Memory).

Date code
A marking on all PCB and DRAM components indicating the manufacturing date of the product.

(Double Data Rate) or SDRAM II--The next generation of the current SDRAM. DDR finds its foundations on the same design core of SDRAM, yet adds advances to enhance its speed capabilities. As a result, DDR allows data to be sent on both the rising and falling edges of clock cycles in a data burst, delivering twice the bandwidth of standard SDRAMS. DDR essentially doubles the memory speed from SDRAMs without increasing the clock frequency.

An individual rectangular pattern on a wafer that contains circuitry to perform a specific function. The internal circuitry is made of thousands of tiny electronic parts. 'Die' refers to a semiconductor component or part that has not yet been packaged (also known as 'IC' (Integrated Circuit) or 'chip').

Die pick-up tool
The bondhead tool on the machine that picks up the die from the precisor and places it on the leadframe.

Die size
The physical measurements of the die.

A material that conducts no current when it has voltage applied to it. Two dielectrics used in semiconductor processing are silicon dioxide and silicon nitride.

Dielectric deposition
A layer of deposited oxide used to isolate metal 1 from metal 2 on double-level metal processes. This must be done in such a way to prevent hillock formation on level 1.

The intermingling of molecules of two or more substances. When high temperature processes are done in diffusion tubes, the high temperature accelerates diffusion. Typical diffusion furnace temperature is 950 degrees Centigrade, or 1742 degrees Fahrenheit.

Dual Inline Memory Module. A printed circuit board with gold or tin/lead contacts and memory devices. A DIMM is similar to a SIMM, but with this primary difference: unlike the leads on either side of a SIMM, which are "tied together" electrically, the leads on either side of a DIMM are electrically independent, ie actually separate circuits which allows for wider and faster data transfer.

(Dual In-line Package) A form of DRAM component packaging. DIPs can be installed either in sockets or permanently soldered into holes extending into the surface of the printed circuit board. The DIP package was extremely popular when it was common for memory to be installed directly on a computer's motherboard.

Data mask signal used by SDRAMs to provide byte masking during write operations. There is one DQM signal for every 8 bits of data width.

Direct address
A computer memory address that is included as part of the instruction.

Direct memory access
A computer feature that allows peripheral systems to access the memory for both read and write operations without affecting the state of the computer's central processor.

Distributed processing
Systems using intelligent input/output controllers and direct - memory - access control to free the CPU of the details of block transfers.

The introduction of an element that alters the conductivity of a semiconductor. Adding boron to silicon will create a P-type (more positive) material, while adding phosphorus or arsenic to silicon will create N-type (more negative) material.

(Dynamic Random Access Memory) DRAM is the most common type of memory and is "dynamic" because in order for the memory chip to retain data, it must be refreshed constantly ( a pulse of current through all of the memory cells every few milliseconds). If the cell is not refreshed, the data is lost. DRAM temporarily stores data in a cell composed of a capacitor and a transistor. Each cell contains a specified number of bits. These cells are accessed by row addresses and column addresses. (See also RAM and SRAM.)


(Direct Rambus DRAM) A totally new RAM architecture, complete with bus mastering (the Rambus Channel Master) and a new pathway (the Rambus Channel) between memory devices (the Rambus Channel Slaves). A single Rambus Channel has the potential to reach 500MBp/s to 800Mb/s in burst mode; a 20-fold increase over DRAM.

Driver board
A printed circuit board that sends signals from the interface board of the oven to the DUT board and back to the interface board. Each oven slot has a corresponding driver board located in the back of the oven.

Dry pack
The process of preparing product for shipment in moisture vapor barrier bags. This process includes tubed or reeled product and a clay desiccant, and an HIC (Humidity Indicator Card), vacuum-sealed in a moisture vapor barrier bag.

Device Under Test. It is used interchangeably with UUT (Unit Under Test).

Type of RAM (Random Access Memory). To keep data in the D(ynamic)RAM memory, this data needs to be 'refreshed' (recharged). The electric charge fades out of a DRAM like air seeps out of a balloon. Because of this change, it is called Dynamic.

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Electrically Erasable PROM.

Electrically Alterable Read-Only Memory.

Error Correction Code. A method used to check the integrity of data stored in memory . ECC memory improves data integrity by detecting errors in memory and is more advanced than parity because it can detect both multiple-bit errors and single-bit errors (parity only detects single-bit errors). ECC is typically found in high-end PCs and file servers where data integrity is key. An ECC scheme capability is partially determined by the sophistication of the "systematic code" employed. The systematic code is like a reference table that the memory system uses to determine whether or not the memory has returned the correct data. Every time data is stored in memory, this code is responsible for the generation of check bits which are stored along with the data. When the contents of a memory location is referenced, the ECC memory logic uses the check bit information and the data itself to generate a series of "syndrome bits". If these syndrome bits are all zeros, then the data is valid and operation continues. If any bits are ones, then the data has an error and the ECC memory logic isolates the errors and reports them in the operating system. In the case of a correctable error, the ECC memory scheme can detect single and double bit errors and correct single bit errors.

A memory feature that allows for faster back to back accesses.

EDO Parity RAM
EDO Parity RAM offers the high performance of EDO memory and has built-in parity which greatly improves reliability. Ideal for high-end PCs and entry-level servers, EDO Parity modules are compatible with any system that accepts a standard 72-pin EDO module and are rapidly becoming the new standard on high-end systems.

(Extended Data Out) EDO RAM is similar to FPM memory, a form of DRAM technology that shortens the read cycle between memory and CPU. but provides improved performance by keeping available data longer in memory. It eliminates much of the wait time by allowing the processor to access data during the refresh cycle. In other words, the computer can load data as it is searching for new information. EDO memory is generally 10 to 20% faster than FPM memory. A computer must support EDO memory in order to notice an increase in performance.

(Enhanced Dynamic Random Access Memory)--a form of DRAM that boosts performance by placing a small complement of static RAM (SRAM) in each DRAM chip and using the SRAM as a cache. Also known as cached DRAM, or CDRAM.

Electrically Erasable Programmable Logic Device. A CMOS PLD made by using EEPROM technology. It can be erased and reprogrammed.

Electrically Erasable, Programmable, Read-Only Memory chip. EEPROMs differ from DRAMs in that the memory stays in even if electrical power is lost. Also, the memory can be erased and reprogrammed.

Electrostatic discharge (ESD)
The dissipation of electricity. ESD can easily destroy semiconductor products.

End Of Buffer.

Electrically Erasable, PROgrammable, Read-Only Memory chip. EEPROMs differ from DRAMs in that the memory stays in even if electrical power is lost. Also, the memory can be erased and reprogrammed.

(ECC on SIMM) A data-integrity checking technology designed by IBM that features ECC data-integrity checking built onto a SIMM.

Erasable Programmable Read Only Memory

The process of applying a cured-plastic protective housing to components. A mold compound. An Assembly step.

A process using a chemical bath (wet etch) or a plasma (dry etch) that removes unwanted substances from the wafer surface.

A local area network allowing several computers to transfer data on a communications cable.

Even Parity
Even parity and odd parity are two different parity protocols used to check the integrity of data stored in memory. A memory manufacturer can use either protocol in a memory product. Even parity adds an additional bit to every byte of data to make the total number of 1's in the segment even. When the byte passes to the CPU, the parity circuit checks the byte to be sure it is still even. If it is, the data is considered to be valid and the parity bit is removed from the byte. If instead it registers as odd, it is considered to be invalid and a parity error is generated.

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Failure rate
Description of the rate at which parts fail, usually expressed as percent per 1,000,000.

Fake Parity
Unlike odd and even parity, fake parity is not capable of detecting an invalid data bit. It was designed to artificially 'satisfy' a parity-enabled computer without actually checking the data for errors. Fake parity attaches a bit to each byte of data just like odd and even parity protocols. The difference is that fake parity simply adds the correct parity bit as the data is sent to the CPU instead of attaching it before the data is stored to memory, and recalculating it before the byte passes to the CPU.

Fall out
Material that fails various tests within the component manufacturing process.

Fine BGA is a ball grid array package with a fine pitch ball arrangement on the underside of the package (larger than CSP).

Failures In Time.

Front Side Bus is the data channel connecting the processor, chipset, DRAM, and AGP socket. FSB is described in terms of its width in bits and it's speed in MHz.

In computing: A status bit that causes some indication of the state or condition of the processing unit.

Flash memory
Flash memory is a non-volatile memory device that retains its data when the power is removed. The device is similar to EPROM with the exception that it can be electrically erased, whereas an EPROM must be exposed to ultra-violet light to erase. Flash memory does not need a constant power supply to retain its data and it offers extremely fast access times, low power consumption, and relative immunity to severe shock or vibration. These qualities combined with its compact size, make it perfect for portable devices like scanners digital cameras, cell phones, pagers, hand-helds and printers. Flash chips have a lifespan limited to 100,000 write cycles, which means flash will never replace main memory in computers.

A Teflon Polyurethane wafer holder used to transport individual wafers. Flatpacks can be stacked to carry and protect several wafers at a time.

A flat, rectangular IC package type with leads sticking out from the sides of the package.

A circuit with two stable states that can be changed from one to the other. Flip-flops are the storage element in most of the SRAMs.

Pertaining to the condition of a device or circuit that is neither grounded nor connected to any potential. (Potential is voltage course or current course).

Floating gate
In Silicon Gate MOS technology: a gate that is not directly connected to the rest of the circuit. Used in EEPROMs.

Fast Page Mode - A common DRAM data-access scheme. Accessing DRAM is similar to finding information in a book. First, you turn to a particular page, then you select information from the page. Fast-page mode enables the CPU to access new data in half the normal access time, as long as it is on the same page as the previous request. This feature is used to support faster sequential access to DRAM by allowing any number of accesses to the currently open row to be made after supplying the row address just once.

Frequency converter
A device or system that can change the frequency of an alternating current, whether or not it changes the voltage or phase.

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Approximately 1 billion bits: 1 bit x 1,024 (that is, 1,073,741,824 bits) Or exactly 2^30 bits.

Gigabyte, GB
A unit of measurement approximately equal to 1024 megabytes. Computer components process data in bytes or multiples of bytes such as kilobytes (~1,000 bytes), megabytes (~1 million bytes), and gigabytes (~ 1 billion bytes).


Gold wire
The wire used to make a physical connection from the device to the leadframe.

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Hard failure
Die that fail functionality testing. These failures have a visual defect 99 percent time, such as poly or metal bridging, missing geometries or layers, particles or contaminates.

Heat sink
A structure, attached to or part of a semiconductor device that serves the purpose of dissipating heat to the surrounding environment; usually metallic. Some packages serve as heat sinks.

Hyper Page Mode also known as EDO.

High Temperature Operating Life.

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I/O port
Connection to a CPU that is configured or programmed to provide data path between the CPU and external devices such as a keyboard, display, or reader; it may be an input port or an output port, or it may be bi-directional.

Integrated Circuit. A tiny complex of electronic components and their connections that is produced in or on a small slice of material (as silicon).

In Circuit Emulator.

Identification Detect. Pins present on DIMMs to provide information to the system using the module.

Standard set by IEEE (Institute of Electrical and Electronics Engineers) for communication between pieces of electronic apparatus.

Infant Mortality
Used to describe the occurrence of premature failures at a higher than normal rate.

A burn-in process whereby electrical functionality of the parts is continuously or periodically monitored and recorded under various voltages, temperatures, and refresh conditions during the burn-in process. This continuous or periodic monitoring of the functionality of each IC allows intelligent decisions to be made.

A PCB that interfaces between the computer and an interface board.

Current x Resistance = Voltage. Also an abbreviation for Infrared.

An amorphous, doped polysilicon used as an underlying layer for the HSG poly to increase conductivity.

International Standards Organization.

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Joint Electron Device Engineering Council - the group that establishes the industry standards for memory operation, features and packaging.

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Notches on a memory module that prevent it from being installed incorrectly or into an incompatible system.

Kilobit Approximately one thousand bits: 1 bit x 210 (that is, 1,024 bits).

Kilobyte, KB
A unit of measurement approximately equal to 1024 bytes. Computer components process data in bytes or multiples of bytes such as kilobytes (~1,000 bytes), megabytes (~1 million bytes), and gigabytes (~ 1 billion bytes).

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L1 cache
Level 1 cache. A small cache integrated in processor that provides a small working space for quick access to the most recently used data.

L2 cache
A specialized memory unit that enhances DRAM performance by providing the CPU with data at speeds ten times faster than DRAM. The L2 cache is comprised of Static RAM (SRAM), a high-speed RAM that does not need to be refreshed to retain its data. Most computers have two different memory caches; L1 cache, located on the CPU, and L2 cache, located between the CPU and DRAM. L1 cache is faster than L2, and is the first place the CPU looks for its data. If data is not found in L1 cache, the search continues to the L2 cache and then to DRAM. In early processors, the L2 cache was not integrated into the processor but rather built into the motherboard, and was in some cases upgradeable. See COAST.

Laser scribe
Process which uses a YAG (Yittrium-aluminum-Garnet) laser to melt the silicon in a dot matrix to form wafer scribe numbers.

Circuit element that stores a given value on its output until told to store a different value.

Latch up
An undesired phenomenon in an integrated circuit whereby a circuit locks in a certain state and will not change.

Latch voltage
The effective input voltage at which a flip-flop changes states.

The metal extensions from an IC package or discrete component that connects the component to the PCB. The leg or contact point of the component that is either physically soldered to a PC board or placed within a socket for connection.

A metal structure that is part of the device. The die is attached to the leadframe.

Leads or Legs: The official name for the metal 'feet' on an IC. Also called 'pins.' The part of the lead assembly that is formed after a portion of the lead frame is cut away. The part's connection to the outside world.

Undesirable conductive paths in components, subsystems, and systems; also the current through such paths.

Life testing
Accelerated testing of electronic components to establish their field reliability.

Linear circuit
A circuit that produces a voltage output approximately proportional to the input voltage, generally over a limited range of voltage frequency.

Linear regulator
Power supply design in which the voltage is held constant by dissipating 50% of the input voltage times and output current as a margin.

Linear selection
A method of selecting memory or input/output devices that dedicates one address line per chip selection; results in overlapping or noncontiguous memory; used because it is the cheapest method of selection.

Locator pin
A pin in the mold which locates the leadframe in the correct position on the mold for processing.

Logic Board
(See motherboard)

Logic circuit
An integrated circuit which provides a fixed set of output signals according to the signals present at the input.

Logic gate
Several individual device functions on an integrated circuit chip.

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Detail test pattern designed to check for decoder and cell interaction problems.

Amount of memory equal to 1 bit x 1,0242 or 1,048,576 bits of information. (Abbreviated Mb.)

Amount of memory equal to 1,048,576 bytes of information. (Abbreviated MB.)

A Term commonly used to refer to computer system's random access memory (see also RAM). The term memory has also been used to refer to all types of electronic data storage (see storage). A computer system's memory is crucial to its operation; without memory, a computer could not read programs or retain data. Memory stores data electronically in memory cells contained in chips. The two most common types of memory chips are DRAM and SRAM.

Memory Bank
A logical unit of memory in a computer, the size of which is determined by the computer's CPU. For example, a 32-bit CPU calls for memory banks that provide 32 bits of information at a time.

Memory Configuration
The amount of memory in an IC and how it is accessed. Also, a code on the lot traveler used to indicate the IC's memory configuration (e.g., 1M1 = 1 Meg x 1, 4M4 = 4 Meg x 4, etc.).

Memory Controller
The logic chip used to handle the I/O (input/output) of data going to and from memory. See chipset.

Memory Cycle
Minimum amount of time required for a memory to complete a cycle such as read, write, read/write, or read/modify/write.

Memory Types:

  • Cache Data SRAM: quick-access chip.

  • DRAM dynamic random access memory.

  • SDRAM synchronous dynamic random access memory.

  • DDR SDRAM double data rate dynamic random access memory.

  • SLDRAM synchronous link dynamic random access memory.

  • RDRAM (also DRDRAM) Rambus dynamic random access memory.

  • EPROM: erasable, programmable, read-only memory.

  • PROM: programmable, read-only memory.

  • RAM: random access memory.

  • ROM: read-only memory (permanent memory that cannot be changed).

  • SRAM: static random access memory.

Megahertz is a measurement of clock cycles in millions of cycles per second.

A unit of measure equivalent to one-millionth of a meter; synonymous with micrometer.

Millions of Instructions Per Second. This measurement is generally used when describing the speed of computer systems.

Metal Nitride Oxide Semiconductor. The technology used for EAROMs (Electrically Alterable ROMs); not to be confused with NMOS.

Moisture vapor barrier bag
A vacuum-sealed bag designed to keep the moisture out so that the parts inside will not be damaged.

Contained on one chip or substrate, as a microprocessor system including not only the logic but also memory or input/output circuits.

Metal-Oxide-Semiconductor. Layers used to create a semiconductor circuit. A thin insulating layer of oxide is deposited on the surface of the wafer. Then a highly conductive layer of tungsten silicide is placed over the top of the oxide dielectric.

MOS device
Device in which current flow occurs in a single channel of P- or N-type material and is controlled by an insulated electrode on the surface of the channel region.

MOS process
The set of chemical and metallurgical steps used to make MOS Large Scale Integration.

Metal Oxide Semiconductor Transistor.

Motherboard (also known as Mainboard)
Also known as logic board, main board, or system board; your computer's main electronics board, which in most cases either contains all CPU, memory, and I/0 functions, or has expansion slots that support them.

Mean Time Between Failures.

Mean Time To Failure.

Memory Unit. Usually a printed circuit board assembly populated with memory chips that stores a certain quantity of memory. Intel term for one of the types of cards in a memory system card set.

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A computer logic circuit that produces an output which is the inverse of that of an AND circuit.

Literal: One-billionth (10 to the -9). Diffusion: A tool used to measure the thickness of a film on a wafer.

One billionth of a meter.

Nanosecond (ns)
One billionth of a second. Memory data access times are measured in nanoseconds. For example, memory access times for typical 30- and 72-pin SIMM modules range from 60 to 100 nanoseconds.

Not Connected.

Negative charge
Charge caused by the presence of electrons, not their absence.

A unit of force in the meter-kilogram-second system needed to accelerate a mass of one kilogram one meter per second per second.

Usually 4 bits or half a byte.

N-channel Metal Oxide Semiconductor. This pertains to MOS devices constructed on a P-type substrate in which electrons flow between N-type source and drain contacts. NMOS devices are typically two to three times faster than PMOS devices.

A term created by Apple Computer, Inc. that describes a memory module which uses 16-Mbit technology. For a given capacity, a noncomposite module will have fewer chips than a composite module.

Nonvolatile memory
Types of memory that retain their contents when power is turned off. ROMs, PROMs, EPROMs and flash memory are examples. Sometimes the term refers to memory that is inherently volatile, but maintains its content because it is connected to a battery at all times, such as CMOS memory and to storage systems, such as hard disks.

Logical NOT-OR.

NS (ns)
Nanosecond (ns). One billionth of a second; used to measure the speed of the parts (e.g., -07 nanoseconds).

Non-Volatile Random Access Memory.

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Odd Parity
Even parity and odd parity are two different parity protocols used to check the integrity of data stored in memory. A memory manufacturer can use either protocol in a memory product. Odd parity adds an additional bit to every byte of data to make the total number of 1s odd. When the byte passes to the CPU, the parity circuit checks the byte to be sure it is still odd. If it is, the data is considered to be valid and the parity bit is stripped from the byte. If instead it registers as even, it is considered to be invalid and a parity error is generated.

Output-Enable. On a part, where data-in and data-out are shared on the same pins, the OE must be triggered to request output data.

A unit of measure of electrical resistance.

A circuit interruption that results in an incomplete path for the current flow. (e.g., an open wire which opens the path of the current).

Operating system
Software controlling the overall operation of a multipurpose computer system, including such tasks as memory allocation, input and output distribution, interrupt processing, and job scheduling.

Operational amplifier
An electronic circuit which amplifies 'linear' (also called analog) signals.

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A conductive bonding island located strategically on circuit chips for inter-connecting circuit elements or for bringing connections from circuit leads to the outside.

The number of bits that can be accessed from one row address.

Page mode
Mode in which if RAS is kept low and the DRAM is given a column-address without being given a new row-address, the chip will remember which row it was on the last time and automatically stay on that row. It is like saying that all the bits along one row are all on the same 'page,' and the part will assume the same page is intended until a different page is specified.

Programmable Array Logic. A device that can be programmed to do certain logic functions. Then a fuse inside of the device can be blown so the programmed information can never be changed. Sometimes called a PLD (Programmable Logic Device) Language.

Parametric fail
A test of the DUT that checks for pin leakage, the amount of current it draws, opens, and shorts.

Parametric test
A test that measures values, also called a dynamic test as opposed to a functional or Go/No-Go test.

A series of voltage and current tests performed on all products in Probe. The test checks for variations in the fabrication process. Test results are used by engineers to modify or correct processes.

A quality control method that checks the integrity of data stored in a computer's memory. Parity works by adding an extra bit of data to each byte to make the total number of 1's either odd or even An error is detected if the parity circuit determines that this number has changed, indicating that some of the data may have been lost or otherwise corrupted. Two different parity protocols exist, even parity and odd parity. Parity protocols are capable of detecting single bit errors only. To enable multiple-bit error detection, manufacturers must use a more advanced form of error checking called Error Correcting Code (ECC). See also Fake Parity.

Parity Bit
A bit added to a group of bits to detect the presence of an error.

The portion of a language translator (compiler or assembler) which determines the logical structure of the program being completed.

Passive device
A device incapable of current gain or switching such as a resistor or capacitor.

Passive element
A circuit element without an energy source such as a capacitor or resistor.

Intel's PC100 specification defines the requirements for SDRAM used on 100 MHz FSB motherboards. Around the middle of 1998, Intel introduced the BX chip set to their motherboard designs. One element in this new architecture will include an increase in the PC main memory bus speed (Host bus) from 66 to 100 MHz, called PC 100. To match the 100MHz bus speed, 100MHz SDRAM modules is the required memory technology for this new chip set.

The PC133 specification details the requirements for SDRAM used on 133MHz FSB motherboards. PC133 SDRAM can be used on 100MHz FSB motherboards but will not yield a performance advantage over PC100 memory at 100MHz.

(Printed Circuit Board) A component made up of layers of copper and fiberglass; the surface of a PCB features a pattern of copper lines, or "traces," that provide electrical connections for chips and other components that mount on the surface of the PCB. Examples: motherboard, SIMM, credit card memory, and so on.

(Personal Computer Memory Card International Association) A standard that allows interchangeability of various computing components on the same connector. The PCMCIA standard is designed to support input/ output devices, including memory, fax/modem, SCSI, and networking products.

Presence Detect. Indicator pins on SIMMs and DIMMs that provide information to the system using the module.

Pin Grid Array.

The metal extensions from an IC package or discrete component that connects the component to the PCB.

Pin one hole
The hole located on the 'pin one' side of the leadframe.

Pin-one indicator
An indentation or mark on the top of the part that indicates where the first lead of the die inside is located.

Pipeline Burst Cache
A type of synchronous cache that uses two techniques to minimise processor wait states - a burst mode that pre-fetches memory contents before they are requested, and pipelining so that one memory value can be accessed in the cache at the same time that another memory value is accessed in DRAM.

Programmable Logic Array. An array of logic elements that can be programmed to perform a specific logic function. It can be as simple as a gate or as complex as a ROM and can be programmed (often by mask programming) so that a given input combination produces a known output function.

Programmable Logic Devices. Devices with 10-100 times higher level of integration than a TTL; called programmable because they can be customized in software rather than in hardware.

P-channel Metal Oxide Semiconductor. This pertains to MOS devices constructed on an N-type silicon substrate in which holes flow between source and drain contacts.

Protective covering over the die; also called Die Coat

Poly-crystalline layer of silicon used for the silicon gate contact in silicon gate MOS devices; also used for interconnections between devices.

Populated board
A PCB with components.

Power down
To turn the system's power OFF.

Power up
To turn the system's power ON.

Plastic Quad Flat Pack. A square, flat package with gullwing leads located around all four sides of the package.

Primary Cache
Cache that is closest to the processor: typically located inside the CPU chip. Can be implemented either as a unified cache or as separate sections for instructions and data. Also referred to as Level 1 cache or internal cache.

Wire used to make electrical contact with a pad on a die; usually made of either beryllium copper, tungsten, or palladium. The diameter of the probe shank is 10 mils, the diameter of the standard probe tip is 1.5 mils, and the length is 7 or 14 mils.

Probe card
A fiberglass card (P.C. Board) that has a hole in the center in which there are pins that are aligned and placed on pads located on the die. As the pins on the probe card are placed on die pads, the probe card tests and sorts die for functionality.

Proprietary Memory
Memory that is custom-designed for a specific computer.

A device or method used to keep the output voltage of a device at a high level; often a resistor network connected to a positive supply voltage.

Printed Wiring Board; board upon which there are layers of printed circuits where DRAMs can be attached with solder so that memory can be accessed.

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Quad flat pack
QFP: A flat, rectangular, integrated circuit with its leads projecting from all four sides of the package without radius.

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Random Access Memory - A type of memory that can be written to and read from in a nonlinear (random) manner. When an application is opened. it is transferred from the hard drive to RAM where it is more readily accessible. RAM enhances system performance because it can process requests from the CPU more quickly than the hard drive. The kind of RAM used in main memory on most computers is Dynamic RAM (DRAM). DRAM stores data as electronic signals. These signals must be constantly refreshed to keep them from dissipating. The more RAM your computer has, the more data it can store at one time and subsequently the more efficiently your computer will operate. The data held in RAM is lost when the computer is turned off. The term random derives from the fact that the CPU can retrieve data from any individual location, or address, within RAM.

A period of time in the oven when the temperature goes up.

Random failure region
The portion of the bathtub curve that represents the useful portion of device life.

The difference between the smallest and largest values in a set of data. This is the simplest measure of variation.

Row-Address-Strobe: the signal that tells the DRAM to accept the given address as a row-address. Used with CAS and a column-address to select a bit within the DRAM.

Rambus DRAM is an evolutionary type of DRAM that uses a 16-18 bit data path and is designed to operate with FSB speed of 800 MHz producing a burst transfer rate of 1.6 gigahertz. Rambus DRAM technology is a system-wide, chip-to-chip interface design that allows data to pass through a simplified bus. Rambus uses a unique RSL (Rambus Signaling Logic) technology. Rambus is available in two flavors: RDRAM and Concurrent RDRAM. The third line extension, Direct RDRAM, was developed in stages and went into production in 1999. In late 1996, Rambus agreed to a development and license contract with Intel that lead to Intel's i820 and i840 chip sets supporting Rambus memory being released in 1999.

Read time
The amount of time required for the output data to become valid once the read and address inputs have been enabled; generally called access time.

A mode of operation used in core memory systems.

Read/write memory
A generic term for Random Access Memories.

An electrical process used to maintain data stored in DRAM. The process of refreshing electrical cells on a DRAM component is similar to that of recharging batteries. Different DRAM components call for different refresh methods.

Refresh rate
This is a count of the number of rows (in thousands) refreshed at a time in a refresh cycle. Common refresh rates are 1K, 2K, and 4K. DRAM stores data as a series of electron charges in individual cells. This data must be constantly recharged or 'refreshed' to keep the data from dissipating. The refresh rate refers to the size of the data that must be recharged, and is typically expressed in kilobytes (~1,000 bytes). Two common refresh rates are 2K and 4K, with 2K being the faster rate.

Registered memory
Registers delay memory information for one clock cycle to ensure all communication from the chipset is collected by the clock edge, providing a controlled delay on heavily loaded memories.

Relative address
An identifier that indicates the position of a memory location in a computer routine relative to the base address as opposed to the memory location's absolute address.

Release time
The amount of time data must remain stable after a device or circuit has been clocked; also called 'hold time.'

A material that prevents etching or plating of the area it covers; also called photoresist.

Rambus Inline Memory Modules used for RAMBUS DRAM. A form of chip packaging that is similar to DIMMs using Direct Rambus DRAM memory subsystems.

Reduced Instruction Set Computing. The design methodology is usually associated with microprocessors. RISC chips use simpler instructions, or commands, than CISC chips. However, they need to use more steps to perform many functions that CISC chips perform in one step. SPARC and MIPS chips are based on RISC.

Rise time
The amount of time required for a signal level change to increase from ten percent to ninety percent of its final specified value.

Returned Material Authorization; required if a customer desires to return products. Also refers to parts that have been returned from a customer.

Read Only Memory - A form of random access memory that can only be read from, not written to. Most systems use ROM to store the instructions a computer needs during the startup process.

Part of the RAM array; a bit can be stored where a column and a row intersect.

Describes how many rows are on a wafer map in the X direction. (X = left to right. Y = top to bottom).

An acronym to represent RS/1 Programming Language. RPLs are functions or procedures written in RS/1's built in programming language. These RPLs are used to automate tasks and analyses.

Read/Write memory.

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A marking on a wafer that identifies the wafer and the lot it came from. The scribe is located on the front of the wafer, opposite the major flat.

Synchronous Dynamic Random-Access Memory. A DRAM technology that uses a clock to synchronize signal input and output on a memory chip. The clock is coordinated with the CPU clock so the timing of the memory chips and the timing of the CPU are "in synch." The synchronization eliminates time delays and allows for fast consecutive read and write capability, thereby increasing the overall performance of the computer. SDRAM has two separate memory banks that operate simultaneously, while one bank prepares for access, the other is being accessed. SDRAM allows the CPU to access memory approximately 25 percent faster than EDO memory because it is controlled by the system clock. SDRAM can only be used in computers designed for it and cannot be mixed with any other type of memory. SDRAM can operate at 100MHz, 133Mhz and features a burst mode that allows it to address blocks of information instead of small data bits.

Secondary Cache
Cache that is second closest to the processor; typically located on the system board. Also referred to as Level 2 cache and external cache.

Self Refresh
A memory technology that enables DRAM to refresh on its own-independent of the CPU or external refresh circuitry. This technology is built into the DRAM chip itself and reduces power consumption dramatically. It is commonly used in notebook and laptop computers.

Soft Error Rate. An error caused by temporary disruption of memory cell.

Serial Presence Detect (SPD)
Serial Presence Detect. An enhanced presence detect that uses an EEPROM to store modules timings, configuration, and the manufacturer's data.

An element, such as silicon, that has intermediate in electrical conductivity between conductors and insulators, which conduction takes place by means of holes and electrons.

Sense amp
The sense amp acts as a distributor of current on the die.

Sense amplifier
A device or circuit capable of sensing very low voltages and amplifying them to some higher voltage level.

Syncronous Graphics RAM. A single port DRAM designed for graphics hardware that require high speed throughput such as 3-D rendering and full-motion video.

A reduction in die (chip) size. A reduction in the size of the circuit design resulting in smaller die sizes that increases the number of possible die per wafer.

Single In-line Module. Same as SIP except with a connector edge instead of leads.

Single In-line Memory Module - a high-density DRAM package alternative consisting of several components connected to a single printed circuit board. A small PCB designed to mount in a socket on a larger PCB providing a large memory upgrade in a small space. This board provides the connection between multiple memory chips and the computer system. SIMMS come in various pin configurations, the most common type being: 30 pin and 72 pin. A 30 pin SIMM has a row of 30 tin or gold pins long the bottom of the module which determine the amount of data the module can handle. These pins connect to only one memory chip as opposed to DIMMs which can connect to multiple chips.

SIMM socket
An interconnect component mounted on the system board, or motherboard, designed to hold a single SIMM.

Single In line Package. A component or module that has one row of leads along one side. Many resistors come in SIP form.

Synchronous Link Dynamic Random Access Memory. SLDRAM is the next evolution of SDRAM using a multiplexed command bus allowing fewer pins to increase bandwidth and allow higher FSB speeds.

Small Outline Dual Inline Memory Module. Smaller and thinner than standard DIMMs, SODIMMs are typically used in laptop computers and mobile computing devices. An enhanced version of a standard DIMM. The small outline DIMM is about half the length of a typical 72-pin SIMM. SO DIMMs come in a variety of pin sizes and can be installed either singly to support 32-bit systems, or in pairs to support 64-bit systems.

Soft error
An error caused by a temporary disruption of the memory cell.

Soft error fail
A part with a temporary, single-bit failure during the soft error test.

Small Outline Rambus Inline Memory Module. SORIMMs have a smaller profile that standard RIMMs and are used in laptop computers and systems that have strict size requirements.

Small Outline J-lead package. A rectangular package with leads sticking out of the side of the package. The leads are formed in a J-bend profile, bending underneath and towards the bottom of the package.

Statistical Process Control. The use of statistics to determine uniformity around a target value.

SPD (Serial Presence Detect)
An enhanced presence detect that uses an EEPROM to store manufacturer data.

The time it takes the RAM to put information into its memory or get information out of its memory. It is measured from the time that an address and proper control signals are given, until the information is stored or placed in the device's output(s).

Speed grade
Our coding for the speed that the stored information in the part can be retrieved by a computer. For DRAMs, a -5 is 50 nanoseconds, a -6 is 60 nanoseconds, a -7 is 70 nanoseconds, etc. For SRAMs, a -10 is 10 nanoseconds, etc.

An operation found in coat and develop programs that stands for spin high speed.

The sudden drastic portion of a pulse that significantly exceeds its average amplitude. Standard deviation A measure of variation for a particular process or product characteristic. This is often abbreviated as 'STD DEV' or 'STD'.

Standard Readability Assessment.

(Static Random Access Memory) An integrated circuit similar to a DRAM (Dynamic Random Access Memory) with the exception that the memory does not need to be refreshed. SRAM is faster and more expensive than DRAM and is generally used for speed-critical areas of the computer such as cache memory.

Starting address
Smallest or lowest address that a memory system will respond to.

Static ram
Unlike volatile memory, static memory retains its contents even when the main current is turned off. The trickle of electricity from a battery is enough to refresh it.

Storage Device
A medium designed to hold data, such as Floppy Diskette, Harrd Disk Drive or CD-ROM.

An input that allows parallel data to be entered a synchronously.

The actual structural material on which semiconductor devices are fabricated, whether passive or active. The term applies to any supportive material, such as the materials used in the fabrication of printed circuits.

Surface-mount package
A J-leaded or Gullwing package or BGA that can be mounted directly on the surface of P.C. Boards (as opposed to through-hole packages).

Switches menu
The menu in BIOS containing user-configurable options for a PC's hardware configuration.

Synchronous Cache
A kind of L2 cache that is synchronized with the CPU. This eliminates the lag time created while the CPU waits for cache memory to fulfill its requests. Synchronous cache is typically 3 to 5 percent faster than asynchronous cache, and is a full 20 percent faster than standard DRAM. See also Asynchronous Cache.

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The subset of the CPU address bits used to compare the tag bits of the cache directory to the main memory address being accessed. Tag memory acts as an index for the information stored in L2 cache.

Cache is physically divided into two sections. The Tag RAM section stores the Tag address of the location of the data in cache. This section is smaller than the Data RAM section, which stores the actual data or instruction.

To Be Determined. Used on quotes in reference to shipping dates.

A measurement of the speed or how fast the part is; it is the time it takes to get a bit of information out of the part after CAS comes down.

Thermal Coefficient of Expansion. A constant that describes the changes in linear dimensions with respect to temperature for a device or material.

A code for TSOP (see TSOP). A package-type code.

Thin Small Outline Package. It is thinner and slightly smaller than an SOJ and with gullwing-shaped leads. A thin, rectangular package with leads sticking out the sides of the package. TSOP DRAM mounts directly on the surface of the printed circuit board. The advantage of the TSOP package is that it is one-third the thickness of an SOJ package. TSOP components are commonly used in small outline DIMM and credit card memory applications.

An electrical process every product goes through which tests the parts for parametric, speed, and functional failures.

A semiconductor device that uses a stream of charge carriers to produce active electronic effects.

Trace Layout
The process of creating a printed circuit on a printed circuit board (PCB).

This number (x8, x9, x32, x36, x64, x72, x80) refers to the bit depth of a module, or to the size of the data path used to access the memory.

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Unbuffered memory
This is where the chipset controller deals directly with the memory. There is nothing between the chipset and the memory as they communicate.

Micron (or micrometer). A unit of length equal to one millionth of a meter.

Microsecond: One millionth of a second.

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Collector Common Voltage.

Volatile Memory
Memory that loses its contents when the power is turned off. A computer's main memory, made up of dynamic RAM or static RAM chips, loses its content immediately upon loss of power. Contrast ROM, which is non-volatile memory.

Video RAM. DRAM with an on-board serial register/serial access memory designed for video applications. VRAM has two separate data ports. One is dedicated to updating the image on the screen while the other one is used for changing the image data stored in memory. This "dual-ported" design gives higher performance than DRAM which cannot read and write simultaneously but is more expensive.

Vss is the abbreviation for the ground on a connection. (Like the ground wire on a battery.)

A condition, transaction, or event that changes or may be changed as a result of processing additional data through a system.

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Write-Enable; WE must be pulsed low when data is written to the chip.

Write time
Time expended from the moment data is entered for storage to the time it is actually stored.

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Zero-page addressing
An addressing mode in which the address is given as an unsigned binary number that specifies one of the memory locations between 0 and 256(decimal).


A unit of measure expressing the intensity of light reflected off an object. 1 lambert = 0.318 foot-candles per square centimeter.
LAN - Local Area Network
A local area network is a group of computers and associated devices that share a common communications line and typically share the resources of a single processor or server within a small geographic area (for example, within an office building).
LCD (Liquid Crystal Display)
Liquid Crystal Display technology is one of the methods used to create flat-panel TVs. Light isn't created by the liquid crystals; a light source (bulb) behind the panel shines light through the display. The display consists of two polarizing transparent panels and a liquid crystal solution (liquid containing rod-shaped crystals) sandwiched in between. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them. Each crystal acts like a shutter, either allowing light to pass through or blocking the light. The pattern of transparent and dark crystals forms the image.
LCD technology is used in direct-view, rear-projection, and front-projection TVs, and is fundamentally different from the CRT technology used in conventional TVs.
LCD projector
Utilizing the LCD technique, these projectors separate the red, green and blue information to three different LCD panels. Since LCD panels do not produce color, the appropriate colored light is then passed through each panel and combined to exit through the projector lens and onto a viewing screen.
LCOS (Liquid Crystal On Silicon) A projection TV display technology
LCOS technology is used in rear-projection, and front-projection TVs. Liquid Crystal on Silicon. This is a reflective display technology where one glass substrate is attached to a silicon chip which is coated with crystals. The chip contains the control circuitry. LD - See Line doubler
Lenticular screen
A screen surface characterized by silvered or aluminized embossing, designed to reflect maximum light over wide horizontal and narrow vertical angles. It must be held very flat to avoid hot spots. A large series of parallel lenticulations cut vertically into the screen surface to improve horizontal dispersion.
A cylindrical lens which causes light passing through it to be dispersed perpendicular to its axis.
The scaling of a widescreen image to fit a standard 4:3 aspect ratio TV screen by shrinking the image so that the width fits exactly. The horizontal black bars that appear above and below the image are actually recorded with the picture, so some of the picture's vertical resolution is lost when you view it. Letterboxing is much more common on DVD movies than VHS videos.
The relative intensity of an audio or video source.
Level control
The level control on some interface products is similar to the contrast control on a data monitor. It can either increase or decrease the output signal level from the interface to a data monitor or projector. This results in greater or less contrast in the picture.
Light emitting diode - LED
A low-power, long life, light source, usually red, green or yellow in color. Some LEDs can produce two different colors.
Light level
The intensity of a given lighting situation as measured in foot-candles (Ft-c).
Light output
Measures the amount of light produced by a front projector. Expressed in "lumens" or "ANSI lumens," with a higher number indicating greater light output.
Line doubler
An Increased Definition Television (IDTV) feature that doubles the number of scan lines in a video picture. This fills the space between the original lines, making them less noticeable and increases the brightness of the picture. For example, the NTSC video field of 262.5 lines is doubled to 525 non-interlaced lines and the PAL field of 312.5 lines becomes 625.
Line level
Audio signal industry-referenced at 600 ohms, 0dB. Consumer systems may use a different reference.
Line out - Audio output
In consumer systems, this may be 10,000 -50,000 ohms, at -10dB or -20dB.
Line voltage
Alternating current (AC) at the level typically found in the home.
The ability of a display device to produce an object the same size anywhere on the screen. For example, poor linearity may show the same line of text one size when it is at the top of the screen, but a different size when it is at the bottom of the screen.
Liquid Audio
More than just a digital audio format, Liquid Audio offers software for music management and playback (Liquid Player), and a network of affiliated web sites (Liquid Music Network) that sell downloadable, copy-protected music. Liquid Audio files usually appear with the .LQT or .LA1 extension. They can utilize several different types of compression, and can come in streaming or downloadable form.
A feature that allows the video signal to be passed through a device relatively unprocessed and sent to a local monitor or other device. The loop-through is separate from the circuits that process a signal for output to the main presentation or recording device(s). Loop-through connections are found on some scan converters and scalers.
When using compression to reduce text and/or graphic files, some techniques "throw away" data in the process. Methods that compress files without losing data are called "lossless". Examples include LZW (Lempel-Ziv Welch), PKZIP or Zip 8-bit.
A term to describe compression techniques that throw away data as part of the process. The more data "loss", the smaller the file, and the lower the quality (grainy or jagged edged) image. Lossy compression methods include JPEG and MPEG. Note: with JPEG, "high" means high compression (greater loss) and "low" means low compression (less loss).
Low impedance
The condition where the source or load is at a lower impedance than the characteristic impedance of the cable. Low source impedance is common; low load impedance is usually a fault condition. Example: 30 - 600 ohms.
LNB (Low Noise Blocker)
The amplifier that blocks low-end frequencies and receives the high-end frequencies used in digital satellite transmissions. This amplifier is located at the end of the arm projecting from the satellite dish.
A single-output LNB dish provides one RF output for connecting an RG-6 coaxial cable to feed the digital signal to a single satellite receiver. A dual-output LNB dish has two RF outputs for distributing satellite signals to two or more receivers.
Luma - Also called Luinance
The photometric radiance of a light source. The luma signal represents brightness in a video picture. Luma is any value between black and white and is abbreviated as "Y". Also see Chroma
Luma delay
A video problem in which the intensity of an object or area is shifted slightly to the right of the color. The color occurs in the correct area of the displayed image, but the luma (intensity) starts later.
Lumen - LM
The unit of measure for light output of a projector. Different manufacturers may rate their projectors' light output differently. "Peak lumens" is measured by illuminating an area of about 10% of the screen size in the center of the display. This measurement ignores the reduction in brightness at the sides and corners of the screen.
The more conservative "ANSI lumens" (American National Standards Institute) specification is made by dividing the screen into 9 blocks, taking a reading in the center of each, and averaging the readings. This number is usually 20-25% lower than the peak lumen measurement. A unit of measure for the amount of light emitted by a source. 0.98 Ft-c (foot-candles) of light covering a surface of 1 square foot.
The brightness component of a color video signal. Determines the level of picture detail. See Luma
The amount of light per square meter, incident on a surface. The term applied to metric measurement of light intensity taken at the illuminated surface. One foot-candle (FT-c) = 10.76 lux, or 1 lux = 1 lumen/square meter = 0.093 foot-candles.
LVDS - Low Voltage Differential Signal
A signal transmission standard developed for the connection of laptop computers to their local LCD displays. National Semiconductor is the manufacturer that is promoting this standard. SGI used LVDS on the 320 and 540 NT Visual Workstations for connection to their 1600SW series, 16x9 aspect ratio, LCD monitor.
Lempel-Ziv Welch. A lossless method of file compression


Absorption: Reduction of acoustical energy usually by converting it into heat via friction using soft, fibrous materials.

AC3: Audio Codec 3. This was the original and more technical name for Dolby Digital. Replaced by marketing mavens when they realized that Dolby's name was not in the title. Some RF modulated, 5.1-encoded laser discs were labeled as AC3. Later versions were labeled as Dolby Digital.

Academy Curve: An intentional roll-off in a theatrical system's playback response above ~2kHz (to -18dB at 8kHz) to minimize noise in mono optical tracks. Some (many) transfers to home video of mono movies have neglected to add the Academy filter during transfer, giving many old movies a screechy sound they were never intended to have. A few home processors have an Academy filter option, making them a must for old-movie buffs. Has been used since 1938.

Acoustic Suspension: A sealed speaker enclosure that uses the air trapped in the cabinet as a reinforcing spring to help control the motion of the woofer(s).

Active: Powered. An active cross-over is electrically powered and divides the line-level signal prior to amplification. An active speaker includes an active crossover and built-in amplifier.

Amplifier: A component that increases the gain or level of an audio signal.

AM: Amplitude modulated.

Anamorphic: Process that horizontally condenses (squeezes) a 16:9 image into a 4:3 space, preserving 25 percent more vertical resolution than letterboxing into the 4:3 space. For the signal to appear with correct geometry, the display must either horizontally expand or vertically squish the image. Used on about two or three promotional laser discs and many DVDs. Also called Enhanced for Widescreen or Enhanced for 16:9.

Aspect Ratio: The ratio of image width to image height. Common motion-picture ratios are 1.85:1 and 2.35:1. Television screens are usually 1.33:1 (also known as 4:3), which is similar to the Academy standard for films in the '50s. HDTV is 1.78:1, or 16:9. When widescreen movies (films with aspect ratios wider than 1.33:1) are displayed on 1.33:1 televisions, the image must be letterboxed, anamorphically squeezed, or panned-and-scanned to fit the screen.

ATSC: Advanced Television Systems Committee. Government-directed committee that developed our digital television transmission system.

Attenuate: To turn down, reduce, decrease the level of; the opposite of boost.

A-Weighting: Measurement based roughly on the uneven frequency sensitivity of the human ear. The influences of low and high frequencies are reduced in comparison to midrange frequencies because people are most sensitive to midrange sounds.

Balanced Input: A connection with three conductors: two identical signal conductors that are 180 degrees out of phase with each other, and one ground. This type of connection is very resistant to line noise.

Bandpass: A two-part filter that cuts both higher and lower frequencies around a center band. A bandpass enclosure cuts high frequencies by acoustic cancellation and low frequencies by natural physical limitations on bass response.

Bandwidth: In audio, the range of frequencies a device operates within. In video, the range of frequencies passed from the input to the output.

Bass: Low frequencies; those below approximately 200 Hz.

Bass Reflex: See Port.

Bipolar: 1) The condition of possessing two pole sets. In a conventional (non-FET) transistor, one pole set exists between the base and collector, and the other pole set exists between the base and emitter. 2) Speakers that consist of two driver arrays facing opposite directions and wired in electrical phase with one another to create a more diffuse soundstage.

Bi-Wiring: A method of connecting an amplifier or receiver to a speaker in which separate wires are run between the amp and the woofer and the amp and the tweeter.

Black Level: Light level of the darker portions of a video image. A black level control sets the light level of the darkest portion of the video signal to match that of the display's black level capability. Black is, of course, the absence of light. Many displays, however, have as much difficulty shutting off the light in the black portions of an image as they do creating light in the brighter portions. CRT-based displays usually have better black levels than DLP, plasma, and LCD, which rank, generally, in that order.

Boost: To increase, make louder or brighter; opposite of attenuate.

Bridging: Combining two channels of an amplifier to make one channel that's more powerful. One channel amplifies the positive portion of an audio signal and the other channel amplifies the negative portion, which are then combined at the output.

Brightness: For video, the overall light level of the entire image. A brightness control makes an image brighter; however, when it is combined with a contrast, or white level control, the brightness control is best used to define the black level of the image (see Black Level). For audio, something referred to as bright has too much treble or high-frequency sound.

Cascading Crossovers: Two crossovers used in series on the same signal in the same frequency range causing greater attenuation of the out-of-band signal. For example, using the crossover in a receiver's bass management setting and the one in a subwoofer simultaneously will create an exaggerated loss of signal.

Cathode Ray Tube: (CRT) Analog display device that generates an image on a layer of phosphors that are driven by an electron gun.

CD: Compact Disc. Ubiquitous digital audio format. Uses 16-bit/44.1-kHz sampling rate PCM digital signal to encode roughly 74 or 80 minutes of two-channel, full-range audio onto a 5-inch disc.

CD-R: Recordable Compact Disc

CD-RW: Rewritable Compact Disc

CEA: Consumer Electronics Association. An association of manufacturers of consumer electronics products.

Center Channel: The center speaker in a home theater setup. Ideally placed within one or two feet above or below the horizontal plane of the left and right speakers and above or below the display device, unless placed behind a perforated screen. Placement is important, as voices and many effects in a multichannel mix come from this speaker.

Channel: In components and systems, a channel is a separate signal path. A four-channel amplifier has at least four separate inputs and four separate outputs.

Chrominance: (C) The color portion of a video signal.

Coaxial: 1) A speaker typically with one driver in the middle of, and on the same axis as, another driver. 2) An audio or video cable with a single center pin that acts as the hot lead and an outer shield that acts as a ground.

Codec: Mathematical algorithms used to compress large data signals into small spaces with minimal perceived loss of information.

Coloration: Any change in the character of sound (such as an overemphasis on certain tones) that reduces naturalness.

Component Video: A signal that's recorded or transmitted in its separate components. Typically refers to Y/Pb/Pr, which consists of three 75-ohm channels: one for luminance information, and two for color. Compared with an S-video signal, a Y/Pb/Pr signal carries more color detail. HDTV, DVD, and DBS are component video sources, though most DBS material is transcoded to component from composite signals.

Compound Loading: See Isobarik.

Composite Video: A signal that contains both chrominance and luminance on the same 75-ohm cable. Used in nearly all consumer video devices. Chrominance is carried in a 3.58-mHz sideband and filtered out by the TV's notch or comb filter. Poor filtering can result in dot crawl, hanging dots, or other image artifacts.

Contrast: Relative difference between the brightest and darkest parts of an image. A contrast control adjusts the peak white level of a display device.

Controller: Generic term that typically refers to a combination preamp/surround processor or receiver. Can also refer to a handheld wireless remote.

Crossover: A component that divides an audio signal into two or more ranges by frequency, sending, for example, low frequencies to one output and high frequencies to another. An active crossover is powered and divides the line-level audio signal prior to amplification. A passive crossover uses no external power supply and may be used either at line level or, more commonly, at speaker level to divide the signal after amplification and send the low frequencies to the woofer and the high frequencies to the tweeter.

Crossover Frequency: The frequency at which an audio signal is divided. 80 Hz is a typical subwoofer crossover point and is the recommended crossover point in theatrical and home THX systems. Frequencies below 80 Hz are sent to the subwoofer; signals above 80 Hz are sent to the main speakers.

Crossover Slope: The rate of attenuation expressed in decibels of change for every octave away from the crossover frequency.

CRT: See Cathode Ray Tube.

Cut: To reduce, lower; opposite of boost.

Damping: Of or pertaining to the control of vibration by electrical or mechanical means.

Damping Material: Any material that absorbs sound waves and eliminates acoustic energy by converting it into a different form. Fibrous material, for example, turns acoustic energy into heat via friction.

D'Appolito: Vertically symmetrical driver array. Typically consists of a tweeter mounted between two woofers. Creates a more-vertically directional sound with evenly spaced lobes in the off-axis response when compared with asymmetrical driver arrays.

DBS: Direct Broadcast Satellite. Term that replaced DSS to describe small-dish, digital satellite systems such as DirecTV and Dish Network.

Decibel (dB): A logarithmic measurement unit that describes a sound's relative loudness, though it can also be used to describe the relative difference between two power levels. A decibel is one tenth of a Bel. In sound, decibels generally measure a scale from 0 (the threshold of hearing) to 120-140 dB (the threshold of pain). A 3dB difference equates to a doubling of power. A 10dB difference is required to double the subjective volume. A 1dB difference over a broad frequency range is noticeable to most people, while a 0.2dB difference can affect the subjective impression of a sound.

Delay: The time difference between a sonic event and its perception at the listening position (sound traveling through space is delayed according to the distance it travels). People perceive spaciousness by the delay between the arrival of direct and reflected sound (larger spaces cause longer delays).

Diaphragm: The part of a dynamic loudspeaker attached to the voice coil that produces sound. It usually has the shape of a cone or dome.

Diffusion: In audio, the scattering of sound waves, reducing the sense of localization. In video, the scattering of light waves, reducing hot spotting, as in a diffusion screen.

Diffusor: Acoustical treatment device that preserves sound energy by reflecting it evenly in multiple directions, as opposed to a flat surface, which reflects a majority of the sound energy in one direction.

Digital Theater Systems: See DTS.

Digital Audio Server: Essentially a hard drive, a digital audio server stores compressed audio files (like MP3 or WMA). Most include the processing to make the files, and all have the ability to play them back.

D-ILA: Direct Drive Image Light Amplifier. This Hughes/JVC technology uses a reflective LCD to create an image. A light source is then reflected off the reflective LCD and is directed through a lens to a screen.

Dipole: Speakers with drivers on opposite faces that are wired electrically out of phase, creating an area of cancellation to the sides. Recommended by THX for use as surround speakers, with null directed at the listener to create a more ambient and non-localizable effect.

Direct-Stream Digital: A format for encoding high-resolution audio signals. It uses a 1-bit encoder with a sampling rate of 2,822,400 samples per second (verses 44,100 for CD). Used to encode six high-resolution channels on SACD.

Direct-View Television: Display whose image is created on the surface from which it is viewed.

Dispersion: The spread of sound over a wide area.

Distortion: Any undesired change in an audio signal between input and the output.

DLP: Digital Light Processing. A Texas Instruments process of projecting video images using a light source reflecting off of an array of tens of thousands of microscopic mirrors. Each mirror represents a pixel and reflects light toward the lens for white and away from it for black, modulating in between for various shades of gray. Three-chip versions use separate arrays for the red, green, and blue colors. Single-chip arrays use a color-filter wheel that alternates each filter color in front of the mirror array at appropriate intervals.

DMD: Digital Micromirror Device. Texas Instruments engine that powers DLP projectors. Uses an array with tens of thousands of microscopic mirrors that reflect a light source toward or away from the lens, creating an image. Each mirror represents a pixel. See DLP.

DNR: Dynamic Noise Reduction. A signal-processing circuit that attempts to reduce the level of high-frequency noise. Unlike Dolby NR, DNR doesn't require preprocessing during recording.

Dolby B: A noise-reduction system that increases the level of high frequencies during recording and decreases them during playback.

Dolby C: An improvement on Dolby B that provides about twice as much noise reduction.

Dolby Digital: An encoding system that digitally compresses up to 5.1 discrete channels of audio (left front, center, right front, left surround, right surround, and LFE) into a single bitstream, which can be recorded onto a DVD, HDTV broadcast, or other form of digital media. When RF-modulated, it was included on some laser discs, which requires an RF-demodulator before the signal can be decoded. Five channels are full-range; the .1 channel is a band-limited LFE track. A Dolby Digital processor (found in most new receivers, preamps, and some DVD players) can decode this signal back into the 5.1 separate channels. Most films since 1992's Batman Returns have been recorded in a 5.1 digital format, though a number of films before that had 6-channel analog tracks that have been remastered into 5.1.

Dolby EX: An enhancement to Dolby Digital that adds a surround back channel to 5.1 soundtracks. The sixth channel is matrixed from the left and right surround channels. Often referred to as 6.1. Sometimes referred to as 7.1 if the system uses two surround back speakers, even though both speakers reproduce the same signal. Software is backwards-compatible with 5.1 systems, but requires an EX or 6.1 processor to obtain additional benefit.

Dolby Pro Logic: An enhancement of the Dolby Surround decoding process. Pro Logic decoders derive left, center, right, and a mono surround channel from two-channel Dolby Surround–encoded material via matrix techniques.

Dolby Pro Logic II: An enhanced version of Pro Logic. Adds improved decoding for two-channel, non-encoded soundtracks and music.

Dome: A type of speaker-driver shape; usually used for tweeters (convex). Concave domes are usually referred to as "inverted domes."

Dope: A tacky substance added to paper cones to damp spurious vibrations that can cause breakup and rough response. Also, see Editor.

Dot Crawl: An artifact of composite video signals that appears as a moving, zipper-like, vertical border between colors.

Driver: A speaker without an enclosure; also refers to the active element of a speaker system that creates compressions and rarefactions in the air.

DSD: See Direct Stream Digital.

DSP: Digital Signal Processing. Manipulating an audio signal digitally to create various possible effects at the output. Often refers to artificially generated surround effects derived from and applied to two-channel sources.

DTS: Digital Theater Systems. A digital sound recording format, originally developed for theatrical film soundtracks, starting with Jurassic Park. Records 5.1 discrete channels of audio onto a handful of laser discs, CDs, and DVDs. Requires a player with DTS output connected to a DTS processor.

DTS ES: An enhanced version of the 5.1 DTS system. Like Dolby's Surround EX, a sixth channel is added. In some cases (DTS ES Discrete), the sixth channel is discrete. Software is backwards-compatible with 5.1 systems, but requires an ES or 6.1 processor to obtain additional benefit. Neo:6 is a subset of DTS ES that creates 6.1 from material with fewer original channels.

DTV: Digital Television. Umbrella term used for the ATSC system that will eventually replace our NTSC system in 2006. HDTV is a subset of the DTV system. While the FCC does not recognize specific scan rates in the adopted DTV system, typically accepted rates include 480i, 480p, 720p, and 1080i.

D-VHS: Digital VHS. Digital signals recorded onto magnetic tape. Greater capacity than typical VHS; can record compressed HDTV signals. See D-Theater

DVD: Officially known as the Digital Video Disc, though marketers unofficially refer to it as the Digital Versatile Disc. DVD uses a 5-inch disc with anywhere from 4.5 Gb (single layer, single-sided) to 17 Gb storage capacity (double-layer, double sided). It uses MPEG2 compression to encode 720:480p resolution, full-motion video and Dolby Digital to encode 5.1 channels of discrete audio. The disc can also contain PCM, DTS, and MPEG audio soundtracks and numerous other features. An audio-only version, DVD-A uses MLP to encode six channels of 24-bit/96-kHz audio.

DVD-A: Digital Versatile Disc-Audio. Enhanced audio format with up to six channels of high-resolution, 24-bit/96-kHz audio encoded onto a DVD, usually using MLP lossless encoding. Requires a DVD-A player and a controller with 6-channel inputs (or a proprietary digital link) for full compatibility.

DVD-R: A recordable DVD format similar to CD-R in that it is a write-once medium. Backed by Pioneer, Panasonic, Toshiba, and others.

DVD-RW: A recordable DVD format similar to CD-RW in that it is re-recordable medium. Backed by Pioneer, Panasonic, Toshiba, and others.

DVD+R: A recordable DVD format similar to CD-R in that it is a write-once medium. Backed by Sony, Philips, Yamaha, HP, and others.

DVD+RW: A recordable DVD format similar to CD-RW in that it is re-recordable medium. Backed by Sony, Philips, Yamaha, HP, and others.

DVD-RAM: A recordable DVD format similar to DVD-RW in that it is a re-writeable format. Unlike DVD-RW it is capable of being written to and erased over 100,000 times. Backed by Hitachi, Panasonic, Toshiba, and others.

DVI: Digital Visual Interface. Connection standard developed by Intel for connecting computers to digital monitors such as flat panels and DLP projectors. A consumer electronics version, not necessarily compatible with the PC version, is used as a connection standard for HDTV tuners and displays. Transmits an uncompressed digital signal to the display. The latter version uses HDCP copy protection to prevent unauthorized copying. See also HDMI.

Dynamic Range: The difference between the lowest and the highest levels; in audio, it's often expressed in decibels. In video, it's listed as the contrast ratio.

EDTV: Extended Definition Television. This CEA-adopted term (though originally mentioned in an April '99 HT article by Mike Wood and Mike McGann) is defined as those products that can display DTV images as 480p or higher.

Efficiency Rating: Level of sound output measured at a prescribed distance with a standard input power. Efficiency rating standard is 1 watt (2.83V at 8 ohms) at 1 meter over a specified frequency range and is measured in decibels.

Electrostatic: One of the oldest speaker design principles, electrostatic speakers are generally comprised of two fixed perforated panels with a constant high-voltage charge applied to them. In between these two panels is an extremely low-mass diaphragm to which the audio signal is applied, causing it to move. There are variations on this construction, but all electrostatic speakers are free from the magnets and voice coils used in conventional speakers.

Enclosure: The container of air that surrounds the rear of a speaker driver.

Enhanced for 16:9: See Anamorphic.

Enhanced for Widescreen: See Anamorphic.

EQ: See Equalization or Equalizer.

Equalization: Loosely, any type of relative frequency adjustment. Specifically, the process of changing the frequency balance of an electrical signal to alter the acoustical output.

Equalizer: A component designed to alter the frequency balance of an audio signal. Equalizers may be graphic, parametric, or a combination of both.

EX: See Dolby EX.

External Crossover: A standalone unit. See crossover.

Feedback: The transmission of current or voltage from the output of a device back to the input, where it interacts with the input signal to modify operation of the device. Feedback is positive when it's in phase with the input and negative when it's out of phase.

Fiber Optic Cable: Glass, plastic, or hybrid fiber cable that transmits digital signals as light pulses.

FireWire: See IEEE 1394.

FM: Frequency Modulated.

Frequency: The number of cycles (vibrations) per second. In audio, audible frequencies commonly range from 20 to 20,000 cycles per second (Hz). In video, frequency is used to define the image resolution. Low-frequency video images depict large objects or images. Higher frequencies depict smaller objects (finer details).

Frequency Response: A measure of what frequencies can be reproduced and how accurately they are reproduced. A measurement of 20 to 20,000 Hz ± 3dB means those frequencies between 20 and 20,000 Hz can be reproduced no more than 3 dB above or below a reference frequency level.

Full-Range: A speaker designed to reproduce the full range (20 Hz to 20 kHz) of audio frequencies.

Gain: Increase in level or amplitude.

Graphic Equalizer: A type of equalizer with sliding controls that create a pattern representing a graph of the frequency-response changes. Raising sliders boosts the affected frequencies; lowering sliders cuts (attenuates) the affected frequencies.

Gray Scale: The ability for a video display to reproduce a neutral image color with a given input at various levels of intensity.

Hanging Dots: An artifact of composite video signals that appears as a stationary, zipper-like, horizontal border between colors.

HDCP: High-Bandwidth Digital Content Protection. Created by Intel, HDCP is used with HDTV signals over DVI and HDMI connections and on D-Theater D-VHS recordings to prevent unauthorized duplication of copyright material.

HDR: Hard-Drive Recorder. Device that uses a computer hard drive to store compressed digital audio and video signals.

HDMI: HDTV connection format using a DVI interface that transfers uncompressed digital video with HDCP copy protection and multichannel audio.

HDTV: High-Definition Television. The high-resolution subset of our DTV system. The FCC has no official definition for HDTV. The ATSC defines HDTV as a 16:9 image with twice the horizontal and vertical resolution of our existing system, accompanied by 5.1 channels of Dolby Digital audio. The CEA defines HDTV as an image with 720 progressive or 1080 interlaced active (top to bottom) scan lines. 1280:720p and 1920:1080i are typically accepted as high-definition scan rates.

Hi-Fi Stereo: Feature found on VCRs that records or plays back stereo soundtracks with improved fidelity compared to using the linear stereo tracks.

High Gain Screen: Material that reflects more light than a reference material. Increases a projector's light output at the expense of uniformity.

High Pass: A filter that passes high frequencies, and attenuates low frequencies. Same as low cut.

Home Theater in a Box: A complete home theater system in one box (or at least sold together as a package). Consists of five or more speakers, a subwoofer, and a receiver. May also include a DVD player.

Horn: A type of speaker that looks like a horn. These speakers have small drivers and very large mouths; the horn shape serves to transform the small radiating area of the driver into the much larger radiating area of the mouth of the horn.

Hz: Hertz or cycles per second. Something that repeats a cycle once each second moves at a rate of 1 Hz.

IEEE 1394: Networking standard for PCs. Combined with 5C copy protection, is used as a two-way connection to transfer the MPEG-compressed digital bitstreams between consumer electronics items, including HDTV tuners and displays, D-VHS recorders, DVD players, and DBS receivers. Also called FireWire, iLink, …

iLink: See IEEE 1394.

Integrated Amplifier: A combination preamp and amplifier.

Interconnects: Any cable or wire running between two pieces of A/V equipment. For example, RCA terminated cables connecting pre/pros and amps.

Interlace: Process of alternating scan lines to create a complete image. In CRT displays, every second field/frame is scanned between the first field/frame. The first field represents the odd lines; the second field represents the even lines. The fields are aligned and timed so that, with a still image, the human eye blurs the two fields together and sees them as one. Interlace scanning allows only half the lines to be transmitted and presented at any given moment. A 1080i HD signal transmits and displays only 540 lines per 60th of a second. 480i NTSC transmits and displays only 240 lines per 60th of a second. Motion in the image can make the fields noticeable. Interlaced images have motion artifacts when two fields don't match to create the complete frame, often most noticeable in film-based material.

Inverted Dome: A type of speaker-driver shape; usually used for tweeters (concave).

Imaging: The ability to localize the individual sound sources in three-dimensional space.

Impedance: A measure of the impediment to the flow of alternating current, measured in ohms at a given frequency. Larger numbers mean higher resistance to current flow.

Isobarik: Also known as compound loading. By using two low frequency drivers (generally mounted face-to-face and wired electrically out-of-phase or mounted front-to-back in a shallow tube and wired electrically in phase) you can halve the volume of the cabinet without reducing the low frequency extension of the subwoofer.

Keystone: A form of video image distortion in which the top of the picture is wider than the bottom, or the left is taller than the right, or vice versa. The image is shaped like a trapezoid rather than a rectangle.

kHz: Kilohertz or one thousand Hz.

Laser Disc: Now-defunct 12-inch disc format with excellent analog, FM-recorded video image, and either analog or CD-quality PCM-encoded audio. Later discs used one of the analog channels to record an RF-modulated Dolby Digital/AC3 soundtrack and/or used the PCM tracks to encoded a DTS soundtrack.

LCD: Liquid Crystal Display. A display that consists of two polarizing transparent panels and a liquid crystal surface sandwiched in between. Voltage is applied to certain areas, causing the crystal to turn dark. A light source behind the panel transmits through transparent crystals and is mostly blocked by dark crystals.

LCOS: Liquid Crystal on Silicon

Letterbox: Format used widely on laser disc and many DVDs to fit wide-aspect-ratio movies (1.85:1 and 2.35:1, for example) into a smaller frame, such as the 1.78:1 area of an anamorphic DVD or the 1.33:1 area of a laser disc or video tape. The image is shrunk to fit the screen, leaving blank space on the top and bottom. This process sacrifices some vertical detail that must be used to record the black bars.

LFE: Low Frequency Effects track. The .1 channel of a Dolby Digital, DTS, or SDDS soundtrack. The LFE is strictly low-frequency information (20 to 120 Hz, with 115 dB of dynamic range) that's added to the soundtrack for extra effect. This track does not inherently contain all the bass of the soundtrack.

Line-Level (Low-Level): A level of electrical signals too low to make the average speaker move sufficiently. Amplifiers receive line-level signals and amplify them to speaker level.

LNB: Low-Noise Blocker. The receiving end of a satellite dish.

Low Pass: A filter that lets low frequencies go through but doesn't let high frequencies go through. Same as high cut.

Luminance: The black and white (Y) portion of a composite, Y/C, or Y/Pb/Pr video signal. The luminance channel carries the detail of a video signal. The color channel is laid on top of the luminance signal when creating a picture. Having a separate luminance channel ensures compatibility with black-and-white televisions.

Megachanger: CD or DVD player with massive disc storage capacity, holding 50 or more discs.

MHz: Megahertz, or 1 million Hz.

Midbass: The middle of the bass part of the frequency range, from approximately 50 to 100 Hz (upper bass would be from 100 to 200 Hz). Also used as a term for loudspeaker drivers designed to reproduce both bass and midrange frequencies.

Midrange: The middle of the audio frequency range. Also used as a term for loudspeaker drivers designed to reproduce this range.

MLP: Meridian Lossless Packing. Encoding format that is able to completely reconstruct the original signal at the receiving end. No information is lost or discarded, regardless of how trivial it might be. Used to encode six channels of high-resolution audio on DVD-A.

Mono: Monophonic sound. One channel.

MP3: MPEG-1 Audio Layer-3. Compression scheme used to transfer audio files via the Internet and store in portable players and digital audio servers.

Multiple-Rate Encoding: Instead of locking encoding at a certain constant data rate, it allows the codec to choose whatever rate is best for that portion of the recording. Usually reduces file size with proportionally less loss in quality.

Multisource: System with multiple sources. Can also be used to describe a receiver that can provide multiple different sources into different rooms.

Multiroom: System that provides audio or video to multiple areas. Usually with only one source.

Multizone: System that provides different sources into multiple areas simultaneously.

N-curve: See Academy Curve.

Negative Gain Screen: Material that reflects less light than a reference material. Often used for DLP and LCD projection systems.

Noise: An unwanted portion of a signal such as hiss, hum, whine, static, or buzzing.

NTSC: National Television Standards Committee. Government-directed committee that established the U.S. color TV standard in 1953. Also known, sarcastically, as Never Twice the Same Color or Never The Same Color due to the inherent difficulty in achieving proper color calibration.

Octave: The difference between two frequencies where one is twice the other. For example, 200 Hz is an octave higher than 100 Hz. 400 Hz is one octave higher than 200 hz.

Ohm: A measure of how much something resists (impedes) the flow of electricity. Larger numbers mean more resistance.

Optical Digital Cable: Fiber optic cable that transfers digital audio signals as light pulses.

Passive: Not active. A passive crossover uses no external power and results in insertion loss. A passive speaker is one without internal amplification.

Passive Radiator: A radiating surface (usually similar to a conventional speaker cone) that is not electrically driven but shares the same air space in a sealed cabinet with an electrically driven loudspeaker. This arrangement is functionally similar to a loudspeaker with a vented (ported) cabinet, with the passive radiator serving the duties of the air in the port.

Parametric: Equalizer with adjust-able parameters, such as center frequency and bandwidth (Q), as well as amplitude.

PCM: See Pulse Code Modulation.

Phase: Time relationship between signals; it's all relative.

Piezo: A type of speaker driver that creates sound when a quartz crystal receives electrical energy.

Pixel: Contraction of picture element. The smallest element of data in a video image.

Plasma: Flat-panel display technology that ignites small pockets of gas to light phosphors.

Port: An aperture in a loudspeaker enclosure that helps extend the usable low-frequency output. A ported enclosure is also called vented or bass reflex.

Power Amp: See Amplifier.

Power Output: A measure, usually in watts, of how much energy is modulated by a component.

Preamplifier: A control and switching component that may include equalization functions. The preamp comes in the signal chain before the amplifiers.

Pre Outs: Connectors that provide a line-level output of the internal preamp or surround processor.

Pre Outs/Main Ins: Connectors on a receiver that provide an interruptible signal loop between the output of the internal preamp or surround processor portion of the receiver and the input of the amplifier portion of the receiver.

Pre/Pro: A combination preamp and surround processor.

Processors: Anything that processes an incoming signal in some way. Surround processors, for example, can decode a Dolby Digital signal to send to an amp so you can hear it.

Progressive Scanning: Each frame of a video image is scanned complete, from top to bottom, not interlaced. For example, 480p means that each image frame is made of 480 horizontal lines drawn vertically. Computer images are all progressively scanned. Requires more bandwidth (twice as much vertical information) and a faster horizontal scan frequency than interlaced images of the same resolution.

Projection System: Display that projects image onto a screen.

Pulse Code Modulation: (PCM) a way to convert sound or analog information to binary information (0s and 1s) by taking samples of the sound and record the resulting number as binary information. Used on all CDs, DVD-Audio, and just about every other digital audio format. It can sometimes be found on DVD-Video.

PVR: Personal Video Recorder. Marketing term for Video HDRs.

Q: The magnification or resonance factor of any resonant device or circuit. Also the width of affected frequencies in an equalizer. Shaped somewhat like an adjustable width bell curve.

RCA Jacks: Receptacles for coaxial cables carrying line-level audio signals. Also called phono-type connectors.

Re-EQ: Short for Re-equalization. A feature found on THX-certified receivers and pre/pros. Movie soundtracks are mixed for theaters or far-field monitors with an expected high-frequency roll-off otherwise known as an X-curve. If these soundtracks are not re-mixed for home use, they will sound too bright when played back through home speakers or near-field monitors. Re-EQ inserts an X-curve response into the signal to compensate for this, which takes out some of the soundtrack's excess edginess or brightness.

Rear-Projection Television: Display that projects an image on the backside of a screen material, usually after having been reflected off of a mirror.

Receiver: Any component that receives, or tunes, broadcast signals, be it NTSC, HDTV, DBS, or AM/FM radio. Typically refers to the single component that includes a preamp, surround processor, multichannel amplifier, and AM/FM tuner.

Resonant Frequency: The frequency at which any system vibrates naturally when excited by a stimulus. A tuning fork, for example, resonates at a specific frequency when struck.

Reverberation: The reflections of sound within a closed space.

Reverberation Time: The amount of time it takes the reverberation to decay 60 dB from the level of the original sound.

RF: Radio Frequency. Television signals are modulated onto RF signals and are then demodulated by your television's tuner. VCRs and DBS receivers often include channel 3 or 4 modulators, allowing the output signal to be tuned by the television on those channels. Also, laser discs used an RF signal for modulating Dolby Digital 5.1 soundtracks on some movies. This requires an RF demodulator (usually referred to as an AC3-RF demodulator) before or in the surround processor to decode the signal.

RGB: Red, Green, Blue. Can refer to an unprocessed video signal or the color points of a display device. Together these three colors make up every color seen on a display device.

Ribbon Speaker: A loudspeaker that consists of a thin, corrugated, metallic ribbon suspended in a magnetic field. The ribbon acts electrically like a low-impedance voice coil and mechanically as a diaphragm.

RMS: Root Mean Square or the square root of the arithmetic mean (average) of the square's set of values. A reasonably accurate method of describing an amplifier's power output.

RPTV: Rear-Projection Television

SACD: Super Audio CD. Enhanced audio format with up to six channels of high-resolution audio encoded using DSD. Requires an SACD player. Multichannel also requires a controller with six-channel analog or proprietary digital inputs for full playback.

Sampling Frequency: How often a digital sample is taken of an analog wave. The more samples taken, the more accurate the recording will be. You need to sample at a minimum of twice the highest frequency you want to capture. For example, the 44.1-kilohertz sampling rate of a CD cannot record sounds higher than 22.05 kilohertz.

Scan Lines: The lines drawn by an electron gun in a CRT system to make up the picture. Drawn horizontally, from left to right, starting at the top left and working to the bottom right.

SDTV: Standard Definition Television. Lower resolution subset of the ATSC's DTV system. 480i is typically accepted as an SD signal. Digital broadcasters can offer multiple sub-programs at SDTV quality, as opposed to one or two HD programs. Digital satellite and digital cable often refer to the majority of their programs as SDTV, somewhat erroneously, as neither system has anything to do with DTV, though both, technically, consist of a digital 480i signal.

Sealed: See Acoustic Suspension.

Sensitivity: A measurement (in dB) of the sound-pressure level over a specified frequency range created by a speaker driven by 1 watt (2.83V at 8 ohms) of power with a microphone placed 1 meter away.

Signal-to-Noise Ratio: A comparison of the signal level relative to the noise level. Larger numbers are better.

Soft-Dome Tweeter: A tweeter that uses a soft fabric or plastic dome as the radiating diaphragm.

Soundfield: The total acoustical characteristics of a space, such as ambience; number, timing, and relative level of reflections; ratio of direct to reflected sound; RT-60 time; etc.

Soundstage: The area between two speakers that appears to the listener to be occupied by sonic images. Like a real stage, a soundstage should have width, depth, and height.

Source: A component from which the system's signals originate. DVD player, AM/FM tuners, and VCRs are sources.

Speaker: A component that converts electrical energy into acoustical energy.

Spider: Part of a loudspeaker driver's suspension that helps center the diaphragm and returns it to rest after being moved by an energized voice coil.

SPL: Sound-Pressure Level. Measured in dB.

Subwoofer: A speaker designed to reproduce very low bass frequencies, usually those below about 80 Hz.

Suspension: The elements that hold a loudspeaker driver's moving parts together, allows them to move, and helps return them to rest. Most commonly, these include the flexible surround around the outer rim of the driver and the spider on the underside of the diaphragm. See Spider.

S-VHS: Super VHS. Enhancement to regular VHS that offers improved luminance resolution. (400 lines or so.)

S-Video: See Y/C.

Tactile Transducer: A device that turns electrical energy into mechanical energy, usually used to shake the seating in a theater. Effective in providing visceral impact without increasing the system's actual SPL level.

THD: Total Harmonic Distortion

3:2 Pulldown Recognition or 3:2 Inverse Telecine: Film is usually recorded at 24 frames per second. NTSC video (North America) is 30 frames (60 fields) per second. In order to get smooth motion, the film frames are broken into video fields in a 3-2-3 sequence. 3 fields for the first film frame, 2 fields for the second film frame, and so on. If a line doubler doesn't compensate for the extra field during playback on a progressive-scan display, the image will have noticeable motion artifacts. A line doubler with 3:2 pulldown recognition or 3:2 inverse telecine can see this sequence in the signal and correct for it by making sure the last field in the first frame isn't mixed with the first field of the second frame.

THX: Certification program for home theater equipment. Uses some proprietary features, but mostly assures a base quality level for a given room size. (See THX Select or Ultra.) Is compatible with any and all soundtrack formats. Stands for either Tom Holman's eXperiment, after the engineer who drafted the original standard, or is named after the company's founder George Lucas' first movie, THX 1138. Nobody agrees on which.

THX Select: Certification program for speakers and receivers that assures a base level of quality and performance when played in a room that's between 2,000 and 3,000 cubic feet.

THX Ultra: Certification program for speakers, receivers, and amplifiers that assures a base level of quality and performance when played in a room that's greater than 3,000 cubic feet.

THX Ultra 2: The newest certification from THX, THX Ultra 2 requires amplification for seven channels, boundary compensation for subwoofers, and stricter requirements for amplifiers and speakers than THX Ultra. Dipole speakers are used for the side surround channels. Monopole speakers are used for the surround back channel and are placed next to each other. The Ultra 2 processor accommodates both 5.1 EX/ES soundtracks, as well as multichannel audio recordings by directing ambient sounds to the dipole speakers and discrete effects/sounds to the back channels.

Transducer: Any device that converts one form of energy into another form of energy, specifically when one of the quantities is electrical. Thus, a loudspeaker converts electrical impulses into sound (mechanical impulses), a microphone converts sound into electrical impulses, a solar cell converts light into electricity, etc.

Transmission Line: A (sub)woofer cabinet design where the driver is mounted at one end of a tube with the same diameter as the radiating area of the driver and a length of 1/4 wavelength of the 3dB down frequency. This "tube" may or may not be round and may be folded to decrease the size of the cabinet.

Tuner: See Receiver.

Tweeter: A speaker driver designed to reproduce high frequencies; usually those over approximately 5,000 to 10,000 Hz.

Uniformity: Even distribution across a given space. In video, uniformity can refer to the distribution of light (hot spotting) or color.

Unity Gain: Output that equals the input. Unity gain screen material reflects as much light as the reference material. Has an even dispersion of light.

Universal Remote: Remote that has the commands of numerous brands stored into memory and can control several different devices simultaneously.

VAS: The volume of air that offers the same degree of restoring force on the loudspeaker driver's cone as that of the cone's suspension.

VCR: See Video Cassette Recorder.

VCR Plus: VCR feature that, once programmed, allows the user to input the TV guide code for a given program into the VCR, which then automatically sets itself to record that program.

Vented: See Port or Passive Radiator.

VHS: Vertical Helical Scan (or as JCV calls it, "Video Home System"). Widely used method of recording audio and video electrical signals onto magnetic tape.

Video Cassette Recorder: Device that records audio and video electrical signals onto magnetic tape (aka videotape recorder).

Volt: The unit of electrical potential, or difference in electrical pressure, expressing the difference between two electrical charges.

Watt: A unit of power or energy. One horsepower is equal to 745.7 watts.

Word Length: The sampling rate determines how often an analog wave is sampled; the word length determines the resolution of the sample. The larger the word length, the more accurate the sample as a whole. A 16-bit word length (CD) allows 65,536 different level or volume steps that can be chosen for each sample.

WMA: Windows Media Audio. An audio compression format similar to MP3, but with digital rights management (copy protection and usage restrictions) built-in by Microsoft.

Woofer: A speaker driver designed to reproduce low frequencies.

Wow-and-Flutter: A measurement of speed instability in analog equipment usually applied to cassette transports and turntables. Wow is slow-speed variations, and flutter is fast-speed variations. Lower percentages are better.

X-over: see crossover.

X-curve: An intentional roll-off in a theatrical system's playback response above ~2kHz at 3dB per octave. A modern convention (standardized between 1975 and 1984) specified in ISO Bulletin 2969, it is measured at the rerecording position in a dubbing stage or two-thirds of the way back in a movie theater. Pink noise should measure flat to 2kHz and then should roll-off above that. Home THX processors add this roll-off, when engaged, so that a home video soundtrack will have the same response as it would in a theatrical setting.

Y/C: Abbreviation for luminance/ chrominance, aka S-video signal. Color and detail signals are kept separate, thus preventing composite video artifacts. Cable uses four-pin connector. Used with S-VHS VCRs, DVD players, Hi-8, and DBS receivers.

Y/Pb/Pr: See component video.

Zone: One or more rooms powered by one or more amplifiers, which are all fed by one source. A home can be divided into multiple zones, which can play multiple sources, even though several rooms (say, the kitchen, dining room, and living room) all play the same source.