Index of Glossary
See also "RAM" and "Frequently Asked Questions"

Access Time
Asynchronous
BEDO
Binary
Bit
Buffering
Byte
"C"
Cache
CAS
Check bits
CMOS
Clock
Clock Speed
CPU
DIMM
DRAM
ECC
EDO
EMM
EMS memory
Extended memory
FPM
Groups
IC
Interleave
JEDEC
Model#
Parity
PCMCIA
PD
Proprietary Memory
RAM
Refresh
SIMM
# Slots
SO DIMM
SOJ
Speed
SRAM
SDRAM
SGRAM
"T"
TSOP
Type
VRAM
XMS memory

Access Time
Time interval between the instant that a piece of information is sent to the memory device and the instant it returns.Back to Index

Asynchronous
Operating mode in which a memory device responds to input signals whenever they occur. As opposed to synchronous operation in which the input signals must be present at specified times in the device's clock cycle.Back to Index

BEDO
Burst EDO DRAM. An EDO DRAM with some burst features such as a four bit burst length that can be delivered in sequential or interleave fashion.Back to Index

Binary
Numbering system using two as a base and requiring only two digits: 0 and 1.Back to Index

Bit
Short for Binary Digit. The smallest piece of data (a 1 or 0) that a computer recognizes. Combinations of 1s and 0s are used to represent characters and numbers.Back to Index

Buffering
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.Back to Index

Byte
A number of binary bits, usually eight, that represent one numeric or alphabetic character.Back to Index

"C"
- Composite; meaning the part is made up of several low density IC's. Also requiring buffers for address and control signals. Items #7310, 10355, and 10390 are composite 64Mb SIMMs and are denoted with a "C" at the end of the description (16x36-60 (36)C). Back to Index

Cache
- (pronounced "cash") - A section of RAM used to store the most frequently accessed data, designed to speed up subsequent access to the same data. Back to Index

CAS
Column Address Strobe. A control pin on a DRAM used to latch 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.Back to Index

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.Back to Index

CMOS
Complementary Metal Oxide Semiconductor. A MOS device containing both N-channel and P-channel MOS active elements. One of two basic processes (MOS and Bipolar) used to fabricate integrated circuits.Back to Index

Clock
A pulse of electricity passed through by wire alternating between high and low voltages. The speed of the clock is measured in terms of Megahertz.Back to Index

Clock speed
A computers internal system clock which the CPU uses to regulate vibrations for measuring speed.Back to Index

CPU
- Central Processing Unit - A chip or circuit that interprets and executes programs by processing a list of machine instructions which perform binary operations on data stored in memory. Back to Index

DIMM
- Dual In-line Memory Module - a particular configuration for RAM consisting of an array of memory chips, IC's, on a small pc board with two rows of I/O contacts. DIMMs have opposing pins on both sides of the circuit board that remain electrically isolated to form 2 separate contacts. This module has 168 pins and can transfer 64,72 and 80 bits at a time. Back to Index

DRAM
- Dynamic Random Access Memory - the most common form of computer memory. DRAM must be refreshed (reenergizing of the capacitors) every 15ms or so. Back to Index

ECC
Error Correction Code. ECC is logic designed to correct memory errors. The number of errors that can be corrected depends upon the algorithms used, and the number of error correction bits (non-data bits) present. This logic may be included on a SIMM, or it may be found on the computer's circuit board. Back to Index

EDO
- Extended Data Output - provides faster access to memory , up to 25%, than standard FPM and reduces the need for second level cache. Generally not compatible with 386's, 486's, and older Pentium machines. Back to Index

EMM
- EMM (expanded memory manager) is a driver that provides a software interface to expanded memory. EMM386.EXE is an example of an EMM that comes with DOS. Back to Index

EMS memory
- EMS(expanded memory specification). Some older programs can use this type of memory. Unlike conventional(the 1st megabyte) or extended memory, expanded memory is not directly addressable by the processor. Instead it can only be accessed through a small 64k window established in the upper memory area (uma). It provides a way for micro computers running under DOS to access additional memory. Back to Index

Extended memory
- Extended Memory is basically all memory past the first megabyte in a PC computer. Back to Index

FPM
- Fast Page Mode - a standard form of memory usually found in 386's, 486's and older Pentium systems. Back to Index

Groups
- The number in this column refers to how many modules must be installed at any one time. Many older machines require sets of two or even four modules to be installed together. Most of the newer (x32,x36,x64) machines allow upgrades one or two modules at a time. Back to Index

IC
- Integrated Circuit - In this case RAM IC's; the small black chips found on SIMMs , DIMMs , and other memory modules.
Click here to see a list of various chip numbers including DRAM, SRAM, and cache. Back to Index

Interleave
The process of taking data bits (singly or in bursts) alternately from two or more memory pages (on an SDRAM) or devices (on a memory card or subsystem). Back to Index

JEDEC
is an organization that establishes standards for memory operation, features, and packaging. Back to Index

Model#
- A specific computer from a particular maker/brand. Back to Index

Parity
- A bit used for error checking in the transmission of data(example: X9, X36, X72).
Back to Index

PCMCIA
Personal Computer Memory Card International Association. A created standard to allow interchangeability of various computer components such as: memory, FAX/modem, SCSI, and networking products all on the same connector.Back to Index

PD
Presence Detect. Indicator pins on SIMMs and DIMMs that provide speed and density information to the system using the memory module.Back to Index

Proprietary Memory
Memory that is designed specifically for a certain computer or printer.Back to Index

RAM
- Random Access Memory - Computer storage that resides on silicon chips; Chips that can store and retrieve data quickly; Code and data that changes while the computer is running.
- RAM sizes - The size of a module listed in megabytes (Mb), or kilobytes (K) or (kb).
- Max RAM - The maximum amount of RAM recognized by a particular machine.
- Base RAM - The amount of RAM on the motherboard itself (permanent RAM). Also, the first 640kb on a PC. Back to Index

Refresh
The process used to restore the charge in DRAM memory cells at specified intervals. The required refresh interval is a function of the memory cell design and the semiconductor technology used to manufacture the memory device. This is a required occurrence used to maintain data stored in DRAM.Back to Index

SIMM
- Single In-line Memory Module - a particular configuration for RAM . An array of memory chips on a small PC board with a single row of I/O contacts. Can be built with a X8, X9, X32, X36 on a board that has 30, 32, or 72 pins. Back to Index

# Slots
- Number of RAM sockets available for upgrading memory. Back to Index

SO DIMM
- Small Outline Dual Inline Memory Module - gold lead, 72 pin - These modules are much smaller than regular DIMMs and are usually used in laptops. It has 32 bit transfer rate.
EDO SO DIMM - Extended Data Output Small Outline Dual Inline Memory Module
SDRAM SO DIMM - Synchronous Dynamic Random Access Memory Small Outline Dual Inline Memory Module. Back to Index

SOJ
Small Outline J-Lead package. This plastic package, designed for memory chips, is a surface mount package with turned under leads that look like the letter J.Back to Index

Speed
- In nanoseconds,(1ns - 1/billionth of a second), the minimum access speed required for the RAM to work properly with a particular machine. Because this is an access time, the lower the number the faster the module. (i.e. - 60ns is faster than 70ns) Back to Index

SRAM
- Static Random Access Memory - A form of high speed memory. SRAM chips function at high speeds and do not require a refresh cycle like standard DRAM. Back to Index

SDRAM
- Synchonous Dynamic Random Access Memory (Synchronous DRAM.) Generally used as cache. This is standard DRAM with the addition of syncronous control logic. By synchronizing all address data and control signals with a single system clock, SDRAM technology enhances performance, simplifies design and provides faster data transfer. Back to Index

SGRAM
- Synchonous Graphics Random Access Memory - A newer type of high speed memory used exclusively for graphics. Back to Index

"T"
- "T" = True; meaning the part is made with the true IC configuration (non-composite).
Items #10395 is a non-composite 64Mb SIMM using True 8x8's and is denoted with a "T" at the end of the description (16x32-60 (32) EDO T). Back to Index

TSOP
Thin Small Outline Package. This plastic package, designed for memory chips has approximately half the height of a standard surface mounted plastic package (SOJ). Back to Index

Type
- This number (x8, x9, x32, x36, x64, x72, x80) actually refers to the bit depth of a module. Back to Index

VRAM
- Video Random Access Memory - A type of memory in a video display adapter used to create the image appearing on the CRT/screen. It uses dual-ported memory allowing simultaneous reads and writes and is faster than dynamic RAM . Back to Index
To see a Macintosh VRAM table click here !

XMS memory
- XMS (extended memory specification) was developed to specify how programs would use extended memory. The XMS specification functions on system based on the 286 or higher and allows real mode program (those designed to run in DOS) to use extended memory and another block of memory usually out of the reach of DOS. Back to Index

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