Information Technology Reference
In-Depth Information
Information in files may be stored on disks or CDs either contiguously
or in blocks; in either case, directories identify the locations of the var
ious parts of the material.
Conceptually, instructions and data are stored in virtual mem
ory while a program runs, but this space may be larger than can
physically fit within a computer's main memory. Thus, pages of vir
tual memory are brought into main memory as needed during pro
gram execution. Similarly, parts of main memory being used most
frequently are usually placed in cache memory for fast retrieval.
Actual processing occurs in the CPU, which contains only a few
storage locations, called registers. Data move between virtual mem
ory and main memory, between main memory and cache, and be
tween cache and registers according to the demands of processing,
and considerable behindthescenes work is involved in keeping all
types of memory up to date.
Over the years, programs, operating systems, and data sets have
become progressively larger, and this has placed increasing demands
on computer memories.
During processing, data may become scattered throughout
disks, and defragmenting a disk can bring related pieces close to
gether to aid performance.
Computer viruses are unwanted or unanticipated programs, of
ten designed to damage a computer or degrade its performance.
Viruses can enter a computer in many ways, and the best defenses
include constant care and vigilence. Antivirus programs can help
identify viruses before they can be run on your computers.
■
Terminology from This Chapter
antivirus program
deleting a file
disk fragmentation
disk directory
disk sector
disk track
erasing a file
file
page
permanent memory
RAM
ROM
thrashing
transitory memory
virtual memory
virus
