Technical Glossary: Memory, Mass Storage, Networking Technology

Application Program

A sequence of programmed instructions that tell the computer how to perform an e nd use task (i.e. accounting, word processing or other work for the computer sys tem user). To use a program, it must first be loaded into MAIN MEMORY from some AUXILIARY MEMORY such as a floppy diskette or hard disk.

A group of disk drives which have been combined into a common Hardware Array or Dual-Level Array and appear as a single LSU (Logical Storage Unit).

Advanced SCSI Architecture. Seagate chipset technology streamlines the internal architecture of the disc drive, dramatically increasing drive performance. Fully compatible with all industry standard SCSI.

(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.

AT Attachment. This term defines the signal and logical protocol described in X3.221 for IDE (Integrated Drive Electronics) peripherals.

AT Attachment Packet Interface. A command protocol used for accessing ATA (IDE) peripheral devices. Widely used on CD-ROM and Tape Backup units attached to ATA bus.

The average time required for any byte of data stored on a disc to rotate under the disc drive's read/write head. Equal to one half the time required for a sing le rotation of the platter.

Disc or tape drive used with a fixed Winchester disc drive to make copies of fil es or other data for off line storage, distribution or protection against accide ntal data deletion from the Winchester drive, or against drive failure.

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.

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.

A variable unit of data transmission speed equal to one bit per second.

A number system like the decimal numbers, but using 2 as its base and having only the two digits 0 (zero) and 1 (one). It is used in computers because digital logic can only determine one of two states - "OFF" and "ON." Digital data is equi valent to a binary number.

(BASIC INPUT OUTPUT SYSTEM) is a program permanently stored in the memory of the computer and is available without an operating system disk. For example it performs the internal self test of the computer and searches for the operating system on the disc drive.

The smallest unit of information a computer processes. A bit can have a value of either 1 or 0.

(Short for bootstrap). Transfer of a disc operating system program from storage on diskette or hard disc drive to computer's working memory.

A temporary data storage area that compensates for a difference in data transfer rates and/or data processing rates between sender and receiver.

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 i nput/output devices, and peripherals.

A single transaction between 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 specificati ons are measured in bytes or multiples thereof (such as kilobytes or megabytes).

Also known as cache RAM; a small, high-speed memory device located between the CPU and the system DRAM. Cache is designed to supply the processor with the most frequently requested instructions and data. Cache memory can be three to five times faster than system DRAM.

Amount of memory (measured in megabytes) which can be stored in a disc drive. Usually given as formatted (see FORMAT OPERATION).

Compact Disc Read Only Memory. A read only storage device which retrieves up to 660 Mbytes of information from a removable laser disk similar to an audio compact disc.

(CPU). The heart of the computer system that executes programmed instructions. It includes the arithmetic logic unit (ALU) for performing all math and logic ope rations, a control section for interpreting and executing instructions, fast main memory for temporary (VOLATILE) storage of an application program and its data.

An integrated circuit fabricated on a chip of silicon or other semiconductor material, e.g., a CHIP is an integrated circuit, a microprocessor, memory device, or a digital logic device.

1)An instruction sent by the central processor unit (CPU) to a controller for execution. 2) English-like commands entered by users to select computer programs or functions. 3) A CPU command, which is a single instruction such as "add two binary numbers" or "output a byte to the display screen."

A term created by Apple(r) Computer, Inc. that describes a memory module that uses older 4-Mbit technology. For a given capacity, a composite module will have more chips than a noncomposite module.

A controller is a printed circuit board required to interpret data access commands from host computer (via a BUS), and send track seeking, read/write, and other control signals to a disc drive. The computer is free to perform other tasks until the controller signals DATA READY for transfer via the CPU BUS.

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.

DAISY CHAIN A way of connecting multiple drives to one controller. The controller drive select signal is routed serially through the drives, and is intercepted by the drive whose number matches. The disc drives have switches or jumpers on them which allow the user to select the drive number desired.

Digital Audio Tape. A storage device that records digital information on magnetic tape measuring 4mm in width.

Information processed by a computer, stored in memory, or fed into a computer.

When the controller has specified all three components of the sector address to the drive, the ID field of the sector brought under the head by the drive is read and compared with the address of the target sector. A match enables access to the data field of the sector.

An organized collection of data stored in DISC FILES, often shared by multiple users., e.g., the Official Airline Guide, which contains up-to-date schedules for all airlines.

(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 read on both the rising and the falling edge of the clock, delivering twice the bandwidth of standard SDRAMS. DDR essentially doubles the memory speed from SDRAMs without increasing the clock frequency.

An electrical signal protocol which transmits information through a current loop rather than by changes in voltage, thereby reducing the susceptibility to electrical in terference. Differential SCSI uses RS-485 transceivers to transfer 10MHz data at distances up to 25 meters (82 feet).

Any system that processes digital binary signals having only the values of a 1 or 0. An example of a non-digital signal is an analog signal which continuously varies, e.g., TV or audio.

(Dual In-line 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 metal leads on either side of a SIMM, which are "tied together" electrically, the leads on either side of a DIMM are electrically independent.

(DOS). A computer program which continuously runs and mediates between the computer user and the APPLICATION PROGRAM, and allows access to disc data by DISC FILE NAMEs.

For rigid discs, a flat, circular aluminum disc substrate, coated on both sides with a magnetic substance (iron oxide or thin film metal media) for non-VOLATILE data storage. The substrate may consist of metal, plastic, or even glass. Surfaces of discs are usually lubricated to minimize wear during drive start-up or power down.

(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.

Direct Memory Access. A means of data transfer between peripheral and host memory without processor intervention.

(Dynamic Random Access Memory)-The most common form of system memory packaging. DRAM can hold a charge (that is, data) for only a short period of time. Therefore, to retain the data it must be refreshed periodically If the cell is not refreshed, the data is lost.

A computer memory device with moving storage MEDIA (disc or tape).

A number representing a standard configuration of physical parameters (cylinders , heads, and sectors) of a particular type of disc drive. Each at system bios contains a list of drive types that the system considers "standard types". These types are not necessarily the same from one bios to the next.

A software routine which receives I/O requests from higher levels within the operating system and converts those requests to the protocol required by a specific hardware device.

(Error Correction Code)-An electronic method of checking the integrity of data stored in DRAM. ECC is a more elaborate error-detection method than parity; it can detect multiple-bit errors and can locate and fix single-bit errors. ECC usually uses three additional bits per byte of data (compared to one additional bit for parity).

(Extended Data Out)-A form of DRAM technology that shortens the read cycle between memory and CPU. On computer systems designed to support it, EDO memory allowsa CPU to access memory 10 to 20 percent faster than comparable fast-page mode chips.

Sometimes drives have the needed data in their buffer so the drive will not have to perform a seek to get the data. If the average seek time of the drive is, say, 20 msec but for half of the data requests the buffer already contains the data, the effective seek time will be about half of 20 msec or 10 msec. It takes almost no time at all (compared to the time it takes to do a seek) for a buffer todeliver its contents, so the average time required drops significantly, in this example by one half.

Enhanced IDE (EIDE) is the market identity given to a collection of four features that are designed to help meet the future needs of market. Enhanced IDE features include: High-capacity addressing of ATA hard drives over 528 Mbytes, fast data transfer rates for ATA hard drives (support for PIO mode 3 up to 13.3 Mbytes per sec), Dual ATA host adapters supporting up to 4 hard disc drives per computer system, nonhard disc ATA peripherals (such as CD-ROM).

(ECC on SIMM)-A data-integrity checking technology designed by IBM that features ECC data-integrity checking built onto a SIMM. Even parity A type of data integrity checking where the parity bit checks for an even number of I's.

Fast ATA is the market identity given to disc drives that support the high-speed data transfers resulting from implementing the industry standard protocols: Programmed input/output (PIO) mode 3, Multiword direct memory access, read/write multiple sectors per interrupt.

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.

The original SCSI specification defined synchronous data transmission speeds of up to 5MHz. By assuming transceivers which provide tighter timing margins, the SCSI-2 standard allows synchronous transfers of up to 10MHz. Devices which utilize these faster timings are called Fast SCSI devices.

The SCSI-3 specification defined synchronous data transmission rates of up to 20MHz. The 20MHz transfer rate provides speeds up to 20MB/s on an 8-bit bus and 40MB/s on a 16-bit bus. Devices that support these timings are called Fast-20 SCSI devices.

FC-AL Fibre Channel Arbitrated Loop. Open industry standard serial interface for high speed systems. You can view Fibre Channel simply as a transport vehicle for the supported command set (usually SCSI commands). In fact, Fibre Channel is unaware of the content of the information being transported. It simply packs data in frames, transports them to the appropriate devices, and provides error checking.

FAT: What the dos-operating systems uses to keep track of which clusters are allocated to which files and which are available for use.

A computer program written into a storage medium which cannot be accidentally erased, e.g., ROM. It can also refer to devices containing such programs.