Filter
Top Products
GLOSSARY
GL – 2
central processing unit (CPU)
The heart of the computer system that executes
programmed instructions. It includes the arithmetic logic
unit (ALU) for performing all math and logic operations, a
control section for interpreting and executing
instructions, internal memory for temporary storage of
program variables and other functions.
channel
A collection of electronic circuits used in the process of
writing and reading information to and from magnetic
media.
character
An ordered collection of bits representing one of a set of
predefined symbols. Often the term is used
interchangeably with byte, but this is inexact.
closed loop
A control technique that enables the positioning system
to correct off-track errors in real time. The actual head
position is monitored and compared to the ideal track
position to determine any position error that might be
occurring. This information is then used to produce a
correction signal (feedback) that goes to the positioner to
correct the error. (See also track following servo).
closed loop servo
A servo control technique that uses position feedback to
correct off-track errors. See Track Following Servo.
cluster
The smallest allocatable unit of disk storage allowed by
MS-DOS; each FAT entry represents one cluster.
controller
An electronic device for connecting one or more mass
storage peripherals (rigid disk drives, tape drives, and
optical disk drives) to the input/output circuits of a host
computer. Controllers vary in complexity, with more
sophisticated units able to buffer and schedule
commands, correct data errors, and bypass media
defects without host intervention.
controller
A miniature CPU dedicated to controlling a peripheral
device, such as a disk drive, tape drive, video display
terminal, or printer. The controller executes commands
from the central processing unit and reissues commands
to the peripheral device.
correctable error
An error that can be overcome by the use of Error
Detection and Correction.
cylinder
On several disk surfaces sharing a common rotational
axis, the aggregate of tracks at a given radial position. A
set of disk tracks that are simultaneously under the set of
read/write heads. This three-dimensional storage volume
can be accessed after a single seek.
cylinder zero
The outermost cylinder in a drive that can be used for
data storage.
DD
DD
D
data
An ordered collection of information. In a specific case, it
is the information processed by a computer.
data separator
An electronic circuit which decodes playback data and
produces separate clock and data bits. Sometimes
incorrectly used to denote data synchronizer.
data synchronizer
An electronic circuit producing a clock signal that is
synchronous with the incoming data stream. This clock
signal is then used to decode the recording code being
used into user data.
data transfer rate
In a disk or tape drive, the rate at which data is
transferred to or from the storage media. It is usually
given in thousands of bits per second (Kbit/second) or
millions of bits per second (Mbit/second).
dedicated landing zone
A designated radial zone on the disk where contact
starting and stopping occur by design.
dedicated servo
A servo scheme in which a prerecorded pattern on an
otherwise unused disk surface provides position
information to the servo circuitry by means of a head
reading that surface.
defect
A magnetic imperfection in a recording surface.
defect management
A general methodology of avoiding data errors on a
recording surface by avoiding the use of known bad
areas of media. Usually defective sectors or tracks are
retired and data are written in alternate locations. Several
algorithms are possible such as “sector slipping,” or
“spare sector per track.”
defect map
A list of defects that fall within a pass/fail criteria of a user.
This list is usually used by an operating system or a disk
drive controller for defect management.
defect skipping
A defect management scheme for avoiding surface
defects. It has data written before and after the defect,
instead of using alternate tracks or sectors to avoid use
of the defective area.
density
Generally, recording density. See areal, bit, and storage
density.
DC erase
The method of erasing a track using a DC write/erase
current through either a Read/Write or Erase head.
digital
Any system that processes digital binary signals (having
only values of a 1 or 0; usually in bits and bytes) rather
than analog signals (signals that can have many values)