Memory Terms Glossary

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A

AGP
See Advanced Graphics Port

AIMM
AGP inline memory module (See Advanced Graphics Port)

Access Time
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.

Advanced Graphics Port
The advanced graphics port (AGP) bus allows the graphics controller to directly access texture map data from the main memory rather than having to move it to the graphic controllers' local memory first. This helps the system increase the speed of processing graphics and allows for a use of a larger portion of memory by "borrowing" storage for texture maps from main memory.

Array
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.

Asynchronous Memory
Memory that is not synchronized with the system clock. EDO and FPM are examples of asynchronous memory.

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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B

BEDO
Burst EDO is a variant on EDO DRAM in which read or write cycles are batched in bursts of four. Burst EDO bus speeds range from 40MHz to 66MHz, as opposed to the 33MHz bus speeds that can be accomplished using fast page mode or EDO DRAM.

BGA
See Ball Grid Array

BIOS
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.

Ball Grid Array
A type of memory chip with solder balls on the underside for mounting. Use of BGA allows die package size to be reduced because there is more surface area for attachment. Smaller packaging allows more components to be mounted on a module, making greater densities available. The smaller package also improves heat dissipation for better performance. See CSP and FBGA.

Bandwidth
A measure of the capacity of data that can be moved between two points in a given period of time.

Bank
1. A slot or group of slots that must be populated with modules of like capacity in order to fulfill the data width requirement of the CPU
2. A segment of memory on a module, sometimes also referred to as a row. Modules are either single or dual banked
3. An internal logic segment in a memory component. For example, a 64Mb SDRAM has 4 banks.

Binary
Numbering system based on two digits: 0 and 1.

Bit
Binary digit. The smallest piece of data (a 1 or a 0) that a computer recognizes.

Block
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.

Buffered Memory
A buffer isolates the memory from the controller to minimize the load on the chip set. It is typically used when the system has a high density of memory and/or when a system has more than 3 memory module sockets.

Burn-in
The process of exercising an integrated circuit at elevated voltage and temperature. This process accelerates failures 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.)

Bus
Circuitry that is used to move data

Byte
A series of 8 bits.

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C

CAS
Column address strobe is the signal which tells the DRAM to accept the given address as a column address. It is used with RAS and a row address to select a bit within the DRAM.

CAS-B4-RAS (CBR)
CAS before RAS. Column address strobe before row address strobe. A refresh technique in which the DRAM keeps track of the next row it needs to refresh.

COAST
Cache on a stick. Coast modules are used to upgrade a motherboard's L2 cache and Tag memory on some socket 7 and older motherboards.

COB
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.

CPU
Central processing unit. The computer chip primarily responsible for executing instructions.

C-RIMM
See Continuity RIMM™

CSP
See Chip Scale Package.

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

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

Check Bits
Extra data bits provided by a module to support ECC.

Chip Scale Package
A type of ball grid array in which the package is roughly the size of the die.

Chip Set
One or more chips on a motherboard that control the data flow between the processor, memory, and the other components of the system.

Chipkill
A trademark term from IBM. Chipkill is an advanced error checking and correcting (ECC) computer memory technology that protects computer memory systems from any single memory chip failure along with multi-bit errors from any portion of a single memory chip. Chipkill capable systems utilize standard ECC UDIMMs to accomplish this.

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.

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

CompactFlash™
A small flash memory module. The memory chips are enclosed in a plastic case and retain data after they are removed from the system. The most common uses for these are in pagers, handheld computers, cell phones, digital cameras, and audio players.

Contacts
See Edge Contacts

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

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

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D

DDR
Double data rate is a type of SDRAM in which data is sent on both the rising and falling edges of clock cycles in a data burst. It is usually referred to as DDR as opposed to DDR SDRAM.

DDR2
Like DDR, DDR2 is a type of SDRAM in which data is sent on both the rising and falling edges of clock cycles in a data burst. DDR2 is the next evolutionary step in the DDR infrastructure and has additional features built into it to allow for increased system performance.

DIMM
Dual inline memory module. A module with signal and power pins on both sides of the board (front and back).

DRAM
Dynamic random access memory. A type of memory component used to store information in a computer system. "Dynamic" means the DRAMs need a constant "refresh" (pulse of current through all of the memory cells) to keep the stored information. (See also RAM and SRAM.)

Die
An individual rectangular pattern on a wafer that contains circuitry to perform a specific function. Die are encapsulated to form the black chips that are then placed on a module.

Dual Banked
A memory module with two banks or rows. See Bank.

Dynamic
Type of RAM (random access memory). To keep data in the DRAM, 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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E

ECC
Error correcting code. Logic designed to detect and correct memory errors.

EDO
Extended data out. An asynchronous DRAM operating mode that improves access times compared to fast page mode (FPM) DRAMs.

EEPROM
Electrically erasable, programmable, read-only memory. EEPROMs differ from DRAMs in that the memory is saved even if electrical power is lost. Additionally, the memory can be erased and reprogrammed repeatedly.

Edge Contacts
See Edge Connector

Edge Connector
Metal tabs on the edge of a printed circuit board (PCB). The edge contacts are the interface between the PCB and the socket that allow the system to communicate with the memory module.

Electrostatic Discharge (ESD)
The dissipation of electricity. (In layman's terms, a "shock.") ESD can easily destroy semiconductor products, even when the discharge is to small to be felt.

Energy Efficient Modules
Specifically designed to lower server power consumption in a data center, energy efficient memory operates at a lower voltage, thereby lowering the energy consumption of the overall memory sub-system.

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

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F

FBDIMM
Fully Buffered Dual In-line Memory Module. Fully Buffered DIMM architecture features an Advanced Memory Buffer (AMB) between the memory controller and the memory module, allowing  serial interface between the memory controller and the AMB. The AMB allows for additional and larger capacity modules to be used compared to non-buffered modules.

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

FPM
Fast page mode - A feature used to support faster sequential access to DRAM by allowing multiple accesses to the currently open row to be made after supplying the row address just once.

FSB
See Front Side Bus.

Flash Card
A small flash memory module. The memory chips are enclosed in a plastic case and retain data after they are removed from the system. The most common uses for these are in laptops, pagers, handheld computers, cell phones, digital cameras, and audio players. There are several different form factors of flash cards, including CompactFlash™, SmartMedia, PCMCIA, and Small Form Factor Flash Card.

Flash Memory
Flash memory is a non-volatile memory device that retains its data after the power is removed.

Front Side Bus
The main highway for data in a PC. It connects the processor, chip set, DRAM, and AGP socket. FSB is described in terms of its width in bits and its speed in MHz.

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G

Gigabit
Amount of memory equal to 1024 Megabits (1,073,741,824 bits) of information. Abbreviated Gb.

Gigabyte
Amount of memory equal to 1024 Megabytes (1,073,741,824 bytes) of information. Abbreviated GB.

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H

HPM
Hyper page mode, also known as EDO.

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I

I/O Port
Connection to a CPU that provides a data path between the CPU and external devices, such as a keyboard, display, or reader. It may provide input only, output only, or both input and output.

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

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J

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

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K

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

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L

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

L2 Cache
Level 2 cache. L2 cache has the same purpose as L1 cache, but is usually not integrated into the processor. L2 cache is traditionally made of SRAM and in socket 7 and older motherboards was in some cases upgradeable. See COAST.

Latency (also called CAS Latency)
The amount of time in nanoseconds (often measured in clock cycles) between a request to read the memory, and when it is actually output. SDRAMs are typically referred to as CL2 or CL3, with CL2 parts being faster.

Lead
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 chip's connection to the outside world.

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M

MHz
See Megahertz

MIPS
Millions of instructions per second. This measurement is generally used when describing the speed of computer systems.

MTBF
Mean time between failures.

MU
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.

Megabit
Amount of memory equal to 1,048,576 bits of information. (Abbreviated Mb.)

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

Megahertz
A measurement of clock cycles in millions of cycles per second.

Memory Configuration
The amount of memory in an IC and how it is accessed.

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

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

Memory Types
Cache: static random access memory containing recently used information
DRAM: dynamic random access memory.
SDRAM: single data rate synchronous dynamic random access memory.
DDR SDRAM: double data rate synchronous dynamic random access memory. Usually referred to as DDR.
SLDRAM: synchronous link dynamic random access memory.
RDRAM: Rambus dynamic random access memory.
RAM: random access memory.
ROM: read only memory (permanent memory that cannot be changed).
SRAM: static random access memory.

Micron
1. A unit of measure equivalent to one-millionth of a meter; synonymous with micrometer.
2. Also the company name of one of the largest memory producers in the world and the parent company of Crucial Technology.

Motherboard
The main printed circuit board in a computer that carries the system buses. It is equipped with sockets to which all processors, memory modules, plug-in cards, daughterboards, or peripheral devices are connected.

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N

Nanometer (nm)
One billionth of a meter.

Nanosecond(ns)
One billionth of a second; used to measure the speed of the parts

Nibble
Usually 4 bits (half a byte).

Nonvolatile Memory
A memory that retains information if power is removed and then reapplied. SRAM and flash are examples of nonvolatile memory

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O

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.

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P

PCB
Printed circuit board. Board that contains layers of circuitry that is used to connect components to a system.

PC100
The PC100 specification defines the requirements for SDRAM modules used on 100MHz FSB motherboards.

PC133
The PC133 specification details the requirements for SDRAM modules 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.

PCMCIA
Personal Computer Memory Card International Association. An industry organization that helps to set standards for flash cards.

PD
See Presence Detect.

Page
The number of bits that can be accessed from one row address. This is also sometimes referred to as a row.

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.

Parity
A bit added to a group of bits to detect the presence of an error. The parity bit looks at the other 8 bits and determines if they are even or odd and correspondingly is a 0 or 1. The system compares the 8 bits with the parity bit. If they both are even or odd, the data is assumed to be correct. If one is even and one is odd, there is an error, and typically the system will fail.

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

Pin
1. The metal extensions from an IC package or discrete component that connects the component to the PCB.
2. Another term for the Edge Contacts on a Memory Module

Populated Board
A PCB with components.

Power Down
To turn the system's power OFF.

Power up
To turn the system's power ON.

Presence Detect
Circuitry on certain memory modules that provides information to the system.

Processor
The primary chip of the system that oversees all the other components of the system.

Pull-up
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.

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Q

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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R

RAM
Random access memory. A data storage device for which the order of access to different locations does not affect the speed of access, except for bursts. Data is typically stored in RAM temporarily for use by the process or while the computer is operating. FPM, EDO, SDRAM, DDR, etc. are all types of RAM.

RAS
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.

RDIMM
Registered Dual In-line Memory Module. Registered (or buffered) memory modules have a register between the DRAM modules and the system's memory controller. These registers serve to provide additional stability within the memory sub-system and allow more memory modules to be used compared to non-registered modules.

RDRAM
Rambus DRAM is a revolutionary type of DRAM that uses a 16-18 bit data path and is designed to operate with FSB speed of 800MHz, producing a burst transfer rate of 1.6 gigahertz.

RIMM
Rambus inline memory modules used for Rambus DRAM.

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.

Refresh
The process used to restore the charge in DRAM cells at specific intervals.

Refresh Rate
A count of the number of rows (in thousands) refreshed at a time in a refresh cycle. Common refresh rates are 1K, 2K, 4K, and 8K.

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.

Row
Part of the RAM array; a bit can be stored where a column and a row intersect. Sometimes also referred to as a page.

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S

SDR
See SDRAM

SDRAM
Synchronous dynamic random access memory delivers bursts of data at high speeds using a synchronous interface. Its is actually SDR SDRAM (single data rate SDRAM) but is usually used to referred to as just "SDRAM."

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

SIM
Single inline module. Same as SIP except with a connector edge instead of leads.

SIMM
Single inline memory module. A high-density DRAM package alternative consisting of several components connected to a single printed circuit board.

SIP
Single inline package. A component or module that has one row of leads along one side.

SLDRAM
Synchronous link dynamic random access memory. SLDRAM is a type of SDRAM that uses a multiplexed command bus allowing fewer pins to increase bandwidth and allow higher FSB speeds.

SODIMM
Small outline dual inline memory module. Smaller and thinner than standard DIMMs, SODIMMs are typically used in laptop computers.

SORIMM
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.

SOJ
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.

SPD
Serial presence detect

SRAM
See static random access memory

Serial Presence Detect
An EEPROM on certain memory modules used to store and provide information to the system using the module.

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

Shrink
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 Banked
A memory module with only one bank or row. See Bank.

Speed
The time it takes to put information into memory or get information out of 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). RAM speed is typically expressed in nanoseconds (lower is faster) for EDO and FPM, and in MHz (higher is faster) for SDR SDRAM, DDR, SDRAM, and RDRAM.

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. Unlike volatile memory (ie, DRAM), SRAM retains its contents even when the main current is turned off.

Synchronous Memory
Memory that has its signals synchronized with the system clock. SDRAM and DDR are examples of synchronous memory types.

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T

TAG
TAG memory acts as an index for the information stored in L2 cache. It is usually composed of SRAM.

TSOP
Thin small outline package. It is thinner and slightly smaller than an SOJ, with gullwing-shaped leads. A thin, rectangular package with leads sticking out the sides of the package.

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U

Unbuffered memory
This is where the chip set controller deals directly with the memory. There is nothing between the chip set and the memory chips on the module as they communicate.

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

ms
A microsecond: One millionth of a second.

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V

VCM
See Virtual Channel Memory.

VRAM
Video RAM. DRAM with an on-board serial register/serial access memory designed for video applications.

Very Low Profile
VLP modules are space-efficient server memory modules which have a lower overall height compared to standard modules and are ideal for data center environments and blade servers.

Virtual Channel Memory
A memory architecture that is a variant of SDRAM, that has not been seen widespread adaptation.

Virtual Memory
This is system memory that is simulated by the hard drive. When all the RAM is being used (for example if there are many programs open at the same time) the computer will swap data to the hard drive and back to give the impression that there is slightly more memory.

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W

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

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X

Y

Z

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