NCR PC4I, Owner'S Manual

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HISTORICAL DATA
1. Disk Drives
a. Fixed disk drives use either a single disk, or a stack of disks (a
disk “pack”). Each disk is a rigid circle of plastic or aluminum
with a metal oxide coating on one or both sides.
Removable disks are disks, or disk packs, that can be
physically removed from the drive.
Fixed disks are disks that are permanently installed in the
drive.
b. Flexible disk drives use a single soft circle of plastic material
with a metal oxide coating on one or both sides. The flexible
disk (diskette) is always removable.
The industry standard sizes of diskettes are 8-inch and
5-1/4-inch.
Either size diskette can be single- or double-density (bits per
inch [bpi] of recorded information), single or double-sided,
and soft-sectored or hard-sectored.
2. Magnetic Tape Drives
a. Devices normally referred to as magnetic tape drives use
reels of industry standard tapes with a metal oxide coating on
one side.
b. Cassette tape drives use industry standard digital cassettes.
c. Cartridge tape drives use industry standard tape cartridges.
General characteristics of external memory are:
1. It is an extension of main memory because information recorded
in external memory is written there initially from internal
memory under CPU control and read back into internal memory
for processing.
2. It is permanent, that means that the information is not erased
from memory when the power is turned off.
3. With the exception of fixed disks, it uses removable, replaceable,
interchangeable storage elements (disks, diskettes, magnetic
tapes). Thus any number of storage elements can be created or
stored, and can be kept for as long as needed.
OWNER'S MANUAL
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