Data Dictionary - A


  • Access Time
  • Abstract Data Type
  • Access Arm
  • Aliasing
  • Altair 8800
  • Ampere (A or amp)
  • AT Computer
  • ATA
  • Average Seek Time

Access Time
The total time by adding seek time with average latency.

Acronym for Advanced Basic Input/Output System, a set of input/output service routines built into the IBM PS/2 microcomputers that use the Micro Channel Architecture. These routines are designed to support multitasking and protected mode - a means of reserving a portion of memory exclusively for a particular program, thus protecting it and its resources from interference by other executing programs.

Abstract Data Type
In programming, a data type that is defined in terms of the information it can contain and the operations that can be performed with it. An abstract data type is more generalized than one constrained by the properties of the objects it contains – for example, the data type “pet” is more generalized than the data types “pet dog,” “pet bird,” and “pet fish.” The standard example used in illustrating an abstract data type is the stack, a small portion of memory used to store information, generally on a temporary basis. As an abstract data type, the stack is simple a structure onto which values can be pushed (added) and from which they can be popped (removed). The type of value, such as integer, is irrelevant to the definition.

The way in which the program performs operations on abstract data types is encapsulated, or hidden, from the rest of the program. Encapsulation enables the programmer to change the definition of the data type of its operations without introducing errors to the existing code that used the abstract data type. Abstract data types represent an intermediate step between traditional programming and object-oriented programming.

Access Arm
The arm that carries the read/write head (S) over the surface of the disk in a disk drive.

In computer graphics, the effect produced when display resolution is too coarse to minimize the jagged, or “stairstep,” appearance of certain design elements, such as diagonal lines, curves, and circles. Aliasing occurs because pixels (dot on the screen) are arranged retangularly, in rows and columns. If this grid is not fine enough, pixels sometimes cannot be darkened (or lightened) in a pattern that the viewer will perceive as a smoother diagonal or curve.

Aliasing is clearly visible on low-resolution screens or when a small portion of a graphics is enlarged to display the individual dots that constitute it.

Altair 8800
A small computer introduced in 1975 by Micro Instrumentation Telemetry Systems of New Mexico. Sold primarily in kit form, the Altair was based on the 9-bit Intel 8080 microprocessor, had 256 bytes of random access memory, received input through a bank of switches on the front panel, and displayed output via a row of light-emitting diodes (LEDs). Although it was short-lived, the Altair is considered to have been the first successful “personal” computer.

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A network of about 60,000 medium-to-large-scale computers established in the 1960s and developed by the Advanced Research Projects Agency Network(ARPA) of the U.S. Department of Defense as a vehicle for enabling universities and research organizations to exchange information freely. Arpanet, although part of the Department of Defense, is not a classified government or military network.

Ampere (A or amp)
unit of measurement for the amount of current that a device draw from the power supply.

AT Computer
Advanced Technology Computer, introducing 16 bits computing.

Also known as IDE. ATA stands for AT Attachment. An interface use to connect hard disk drives, CD-ROM drives, etc. ATA-1 supports 8/16-bit interface that transfer up to 8.3MB/s, and PIO modes of 0, 1, and 2. It is a standard under the ANSI document number X3.221-1994 (which approved on 12 May 1994), and originated from Compaq, Western Digital Corporation, and Control Data Corporation.

Technology advancement

ATA-2 / Fast ATA / Ultra ATA


ANSI X3.279-1996 ANSI X3.298-1997 ANSI NCITS 317-1998 ANSI NCITS 340-2000 ANSI NCITS 347-2001
Added PIO modes 3 and 4, which transfer up to 16.6MB/s, and DMA modes 1 and 2. LBA supports hard disk up to 8.4GB. Added security features and the S.M.A.R.T (Self-Monitoring, Analysis, and Reporting Technology )feature. Added ATAPI packet command, and UDMA/33, which transfer up to 33MB/s. Added Ultra-DMA/66, which transfer data up to 66MB/ss. Introduce 80 cores ribbon cables. Added Ultra-DMA/100, and transfer data up to 100MB/s.

ATAPI - AT Attachment Packet Interface, ATAPI is an extension of ATA to allow support of devices such as CD-ROM drives, Tape drives, Zip drives, etc.

Average Seek Time - See seek time

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