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Glossary of Terms
bit — The smallest fragment of computer information. Usually represented by a logical 1 (one) or 0 (zero).
byte — Usually a contiguous group of bits, usually 8, that represent a complete piece of usable computer information. Typically, an individual character, such as the letter 'A', can be represented in a single byte.
DIMM (Dual In-line Memory Module) — Pronounced "dimm." A memory device that consists of a PCB board with a row of contact points on both sides of the PCB and several memory chips, usually DRAM, attached to the PCB. The PCB board provides the connection between the multiple memory chips and the computer system in a single component versus the numerous components required when using individual chips. The term generally refers to the 168-pin DIMM module based on a JEDEC specification. See also SIMM and SO DIMM.
DRAM (Dynamic Random Access Memory) — Pronounced "dee-ram." The volatile memory used to temporarily store data in personal computers. DRAM stores each bit of information in a "cell" composed of a capacitor and a transistor. Since the capacitor in a DRAM cell can hold a charge for only a few milliseconds, DRAM must be continually refreshed, or recharged, to retain its data. Static RAM, or SRAM, requires no refresh and delivers better performance, but it is more expensive to manufacture. See also EDO RAM and SRAM.
EDO RAM (Extended Data-Out Random Access Memory) — A form of DRAM that speeds accesses to consecutive locations in memory by assuming that the next memory access will target an address in the same transistor row as the previous one and latching data at the output of the chip so it can be read even as the inputs are being changed for the next memory location. EDO RAM can reduce memory access times compared with standard DRAM chips of the same speed and costs only a little more to manufacture.
EDRAM (Enhanced Dynamic Random Access Memory) — A form of DRAM that boosts performance by using a comparatively small amount of static RAM (SRAM) in each DRAM chip as a cache. Also known as cached DRAM, or CDRAM.
EEPROM (Electrically Erasable Programmable Read-Only Memory) Pronounced "ee-ee-prom." Read-Only Memory (ROM) that can be erased and rewritten electrically. EEPROM is frequently used for system-board BIOSes to permit a computer's BIOS to be updated without replacing the chips. See also ROM and BIOS.
EIDE (Enhanced Integrated Device Electronics or Enhanced Intelligent Drive Electronics) — An enhanced version of the IDE drive interface that expands the maximum disk size, increases the maximum data transfer rate, and supports up to four drives per PC (as opposed to two in IDE systems). See also IDE and SCSI.
EISA (Extended Industry Standard Architecture) — Pronounced "ee-suh." A 32-bit bus architecture developed by a consortium of computer vendors, including Compaq, to counter IBM's proprietary Micro Channel (MCA) architecture. Unlike Micro Channel, EISA is backward-compatible with cards designed for the ISA bus. Like MCA, EISA never gained wide market acceptance.
EMS (Expanded Memory Specification) — A bank-switched memory management scheme developed by Intel, Lotus, and Microsoft that allows MS-DOS applications (normally limited to 640K of memory) to access vast quantities of memory. Memory that conforms to this standard is often referred to as expanded memory. EMS memory is rarely used today, as protected-mode operating systems such as Windows, makes it obsolete.
EPROM (Erasable Programmable Read-Only Memory) — Pronounced "ee-prom." Read-Only Memory (ROM) that can be erased by high-intensity ultraviolet (UV) light and then rewritten, or "reprogrammed." EPROM chips normally contain UV-permeable quartz windows to permit exposure for erasing the program that also exposes the chips' internals. This window is usually covered. See also ROM and EEPROM.
IDE (Integrated Device Electronics or Intelligent Drive Electronics) — A hard drive-interface specification that integrates all the drive control electronics on the drive itself, rather than on the adapter connecting the drive to the expansion bus. This integration shortens the signal paths between drive heads and controller, permitting higher data transfer rates and simplifying adapter cards. The IDE specification has replaced the Enhanced Small Device Interface (ESDI) specification that has mose of the drive electronics on the controller card. See also EIDE and SCSI.
I/O (input/output) — A general term that describes any action that sends and receives data on a computer. The term "file I/O," for example, refers to the act of reading or writing information in a disk file.
IRQ (Interrupt ReQuest) — A signal from a hardware device such as a keyboard or a drive controller indicating that it needs the CPU's attention. IRQ signals are transmitted along IRQ lines, which connect peripheral devices to an interrupt controller. The interrupt controller prioritizes the incoming interrupt requests from the different devices and delivers them to the CPU.
RAM (Random Access Memory) — Pronounced "ram." The generic term for memory used in modern computers that can be read from and written to in a direct, or random, method. RAM comes in many forms, and manufacturers are continually coming up with new designs to provide the fastest possible access times at the lowest possible cost. See also DRAM, EDO RAM, SRAM.
ROM (Read-Only Memory) — Pronounced "romm." The generic term for the non-volatile memory that can be read from but not written to. A computer's BIOS is typically contained in ROM. By using ROM, the code and data in the ROM BIOS need not be reloaded each time the computer is started, and they're protected from corruption caused by malfunctioning applications that attempt to write into the wrong part of memory. Some forms of ROM can be rewritten by applying higher-than-normal voltages to the inputs and holding the voltages for several milliseconds. See also BIOS, EPROM, and EEPROM.
SIMM (Single In-line Memory Module) — Pronounced "simm." A memory device that consists of a PCB board with a single row of contact points and several memory chips, usually DRAM, attached to the PCB. The PCB board provides the connection between the multiple memory chips and the computer system in a single component versus the numerous components required when using individual chips. See also DIMM and SO DIMM
SLIP (Serial Line Internet Protocol) — Pronounced "slip." A protocol used to connect a personal computer to the Internet through a dial-in connection. SLIP is also used to run TCP/IP over phone lines. See also PPP and TCP/IP.
SO DIMM (Small Outline Dual In-line Memory Module) — Pronounced "es-oh dimm." A memory device that consists of a PCB board with a row of contact points on both sides of the PCB and several memory chips, usually DRAM, attached to the PCB. The PCB board provides the connection between the multiple memory chips and the computer system in a single component versus the numerous components required when using individual chips. The term generally refers to the 72-pin SO DIMM module based on a JEDEC specification. See also SIMM and DIMM.
SRAM (Static Random Access Memory) — Pronounced "es-ram." A form of RAM that retains its data without the constant refreshing, or recharging, that DRAM requires. SRAM is generally preferable to DRAM because it offers faster memory access times (a critical element in a PC's performance), but it is also more expensive to manufacture because it contains more electrical components. The most common use for SRAM is to cache data traveling between the CPU and a RAM subsystem populated with DRAM to boost performance by reducing the number of DRAM accesses required. See also DRAM.
UMB (Upper Memory Block) — A block of memory (between 640K and 1MB) created in upper memory by a 386 memory manager. This is useful for loading TSRs and device drivers so they don't occupy the limited memory below 640K. See also TSR.
WRAM (Windows Random Access Memory) — Pronounced "double-you-ram." Similar to VRAM, but with added logic designed to accelerate common video functions such as bit-block transfers and pattern fills. WRAM is priced competitively with VRAM and can substantially speed up certain graphical operations such as video playback and screen animation. See also VRAM.
XMS (Extended Memory Specification) — A memory allocation scheme that allows programs to use extended memory (memory above 1MB) without interfering with each other. Access to XMS memory is facilitated by an XMS driver such as Microsoft's HIMEM.SYS, which is supplied with Windows.