Английский для пользователей компьютеров. Ч.1. Белобородова М.Л - 20 стр.

Basically there are two types of storage: primary storage (also called main
memory, internal memory, or memory), where data is volatile, and secondary
storage (also called auxiliary storage), where data is nonvolatile. If data is
volatile, it is lost when the power to the computer is turned off; nonvolatile data
remains intact.
In storage, data is represented using a binary code, a system of combinations of
binary digits (bits)—0, meaning "off" (no magnetic spot present), and 1, meaning
"on" (magnetic spot present). Two common binary coding schemes are the
American Standard Code for Information Interchange (ASCII) and the Extended
Binary Coded Decimal Interchange Code (EBCDIC). ASCII is typically used to
represent data on microcomputers, and EBCDIC is used on larger computers.
Data is stored in files, which can be understood by means of the data storage
hierarchy. A file is a collection of records; a record is a collection of fields, which
comprise a collection of bytes. A byte, or a character, is a collection of 8 bits. A
nineth bit—the parity bit—may be added as an error-checking device. Files can
be categorized as follows: (1) transaction file, (2) master file, (3) report file, (4)
output file, (5) history file, and (6) backup file.
The three methods used to store and retrieve data in files are: sequential, direct,
and indexed sequential. In the sequential method, data can be retrieved only in
the order in which it is stored. All records must be read to get to the data you
want. Direct access avoids that problem by allowing you to go straight to the
data you want. Key fields are used by the computer as identifiers to locate the
data. The indexed sequential method allows both sequential and direct access
through the use of an index set up by the computer according to key fields and
locations on the storage media. Your business needs should determine the type
of storage and retrieval method you use.
Introduced in the early 1950s, magnetic tape quickly overcame the limitations of
punched cards as a storage medium. On magnetic tape, data is stored only in
sequential fashion using either the ASCII or EBCDIC coding schemes.
Unfortunately, data put on tape can't be reorganized or altered without creating a
new tape. Because of their limitation, direct access storage media were developed
for microcomputers, including diskettes, hard disks, hard cards, and optical disks.
The direct access storage media used with the larger computers include removable
disk packs, fixed disks, and disk cartridges.
Data is stored on disk surfaces in sectors and tracks. Higher track density (tracks
per inch) and higher recording density (bits per inch) both result in greater
amounts of data per disk. Storage capacity is measured in thousands of bytes