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B

Bandwidth
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.

BIOS
(Basic Input-Output System) - Startup routines that prepare the computer for operation.

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. Modules that are "buffered" usually have small buffer chips mounted on them. Buffered and unbuffered memory cannot be mixed.

Bus
A data path in a computer, consisting of various parallel wires to which the CPU, memory, and all input/output devices are connected.

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C

Cash 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.

CAS Latency
The ratio between column access time and clock cycle time. CAS Latency 2 (CL2) offers a slight performance increase over CAS Latency 3 (CL3).

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.

Compact Flash
A small, lightweight form factor for removable storage cards. CompactFlash cards are durable, operate at low voltages, and retain data when power is off. Uses include digital cameras, cell phones, printers, handheld computers, pagers, and audio recorders.

Continuity Module (Rambus)
A Direct Rambus memory module that does not contain memory chips. TSRIMM provides a continuous channel for the signal. In a Direct Rambus system, open connectors must be populated with TSRIMMs.

Credit Card Memory
A type of memory typically in laptop and notebook computers. Credit card memory is the size of a credit card.

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D

DDR
(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.

DIMM
(Dual In-line Memory Module) - A printed circuit board with gold contacts and memory devices. A DIMM is similar to a SIMM, but with this primary difference: unlike the metal leads on either side of a SIMM, which are "tied together" electrically, the leads on either side of a DIMM are electrically independent.

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E

ECC
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.

EDO
(Extended Data-Out) - A DRAM technology that shortens the read cycle between memory and CPU. On computers that support it, EDO memory allows a CPU to access memory 10 to 20 percent faster than comparable fast-page mode memory.

EEPROM
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.

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F

Flash Memory
Flash memory is considered a solid state storage device. Solid state means that there are no moving parts -- everything is electronic instead of mechanical.
Here are a few examples of Flash memory:
§ Your computer's BIOS chip
§ CompactFlash (most often found in digital cameras)
§ SmartMedia (most often found in digital cameras)
§ Memory Stick (most often found in digital cameras)
§ PCMCIA Type I and Type II memory cards (used as solid-state disks in laptops)
§ Memory cards for video game consoles

FPM
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. Fastpage 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.

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G

Gigabit
Approximately 1 billion bits, or exactly 1 bit x 1,0243 (1,073,741,824) bits.

Gigabyte
Approximately 1 billion bytes, or exactly 1 byte x 1,0243 (1,073,741,824) bytes.

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H

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.

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I

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

Interleaving
Techniques for increasing memory speed. For example, with separate memory banks for odd and even addresses, the next byte of memory can be accessed while the current byte refreshes.

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J

JEDEC
(Joint Electron Device Engineering Council) - An Electronic Industries Alliance (EIA) body that sets semiconductor engineering standards.

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K

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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L

L1 Cache
Also known as primary cache, L1 Cache is a small amount of high-speed memory that resides on or very close to the processor. L1 Cache supplies the processor with the most frequently requested data and instructions.

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.

Lead
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.

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M

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

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

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.

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N

Non-Composite
An Apple Computer, Inc. term for a memory module that used a new technology and contained fewer but higher-density chips. Non-composite modules were more reliable and more expensive than composite modules.

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

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O

Odd Parity
Data integrity checking that adds a single bit to each byte of data. The parity bit is used to detect errors in the other 8 bits.

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P

Parity
Data integrity checking that adds a single bit to each byte of data. The parity bit is used to detect errors in the other 8 bits.

PCB
(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.

PCMCIA
(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.

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R

RAM
(Random-Access Memory) - A memory cell configuration that holds data for processing by a central processing unit (CPU). Random means the CPU can retrieve data from any address within RAM.

Refresh Rate
The number of DRAM component rows that must be refreshed. Three common refresh rates are 2K, 4K and 8K. 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.

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

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S

SDRAM
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.

Serial Presence Detect (SPD)
An EEPROM chip that contains information about size and speed, as well as other specifications and manufacturer information of a memory module.

SGRAM
(Synchronous Graphics Random-Access Memory) - Video memory that includes graphics-specific read/write features. SGRAM allows data to be retrieved and modified in blocks instead of individually. Blocking reduces the number of reads and writes the memory must perform and increases the performance of the graphics controller.

SIMM
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.

SODIMM
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 mall 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.

SOJ
(Small-Outline J-lead) - A common form of surface-mounted DRAM packaging. An SOJ is a rectangular package with J-shaped leads on the two long sides.

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T

TSOP
(Thin Small-Outline Package) - A DRAM package that uses gull wing leads on both sides. TSOP DRAM mounts directly on the surface of the printed circuit board. The TSOP package is one-third the thickness of an SOJ. TSOP components commonly occur in small-outline DIMMs and credit card memory.

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U

Unbuffered Memory
Memory that does not contain buffers or registers located on the module. Instead, these devices are located on the motherboard.

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V

VRAM
(Video Random-Access Memory) - Dual-ported (two separate data ports) memory typically on a video or graphics card. One port is dedicated to the CRT and refreshes and updates the image. The second port is for the CPU or graphics controller and changes the image data in memory.

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