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GLOSSARY

GL – 3

EXTRA PULSE

Term used in surface certification. It is when a flux field
discontinuity remains after the recording surface is erased, thereby
producing an electrical output of a read head passing over the area
with the discontinuity. An extra pulse occurs when the electrical
output is larger than a specified threshold.

FFFFF

FEEDBACK

In a closed-loop system, the output signal (from the servo head) is
used to modify the input signal (to the positioner).

FETCH

A read operation and its related data transfer operations.

FILE ALLOCATION TABLE (FAT)

Allocates space on the disk for files, one cluster at a time; locks out
unusable clusters; identifies unused (free) area; and lists a file’s
location. With two FAT’s present, the second copy ensures
consistency and protects against loss of data if one of the sectors
on the first FAT is damaged.

FLUX CHANGES PER INCH

Synonymous with frpi (flux reversals per inch). Only in MFM recording
does 1 fci equal 1 bpi (bit per inch). In run-length-limited encoding
schemes, generally 1 fci equals 1.5 bpi.

FORMAT

In a disk drive, the arrangement of data on a storage media. A
standard 5.25-inch disk format consists of 17, 26, or 36 sectors per
track, and 512 bytes of data per sector, plus identification, error
correction, and other bytes necessary for accessing and
synchronizing data.

FORMATTED CAPACITY

The actual capacity available to store data in a mass storage
device. The formatted capacity is the gross capacity, less the
capacity taken up by the overhead data used in formatting the
sectors.

FREQUENCY MODULATION

A recording code. A flux reversal at the beginning of a cell time
represents clock bit; a “1” bit is a flux reversal at the center of the
cell time, and a “0” bit is an absence of a flux reversal.

FREQUENCY RESPONSE

A measure of how effectively a circuit or device transmits the
different frequencies applied to it. In disk and tape drives this refers
to the read/write channel. In disk drives, it can also refer to the
dynamic mechanical characteristics of a positioning system.

GGGGG

GIGABYTE (GB)

One billion bytes (one thousand megabytes) or 10

HHHHH

HARD ERROR

An error that is not able to be overcome by repeated readings and
repositioning means.

HARD SECTORED

A technique where a digital signal indicates the beginning of a
sector on a track. This is contrasted to soft sectoring, where the
controller determines the beginning of a sector by the reading of
format information from the disk.

HEAD

The electromagnetic device that write (records), reads (plays back),
and erases data on a magnetic media. It contains a read core(s)
and/or a write core(s) and/or erase core(s) which is/are used to
produce or receive magnetic flux. Sometimes the term is all inclusive
to mean the carriage assembly which includes the slider and flexure.

HEAD CRASH

The inadvertent touching of a disk by a head flying over the disk
(may destroy a portion of the media and/or the head).

HEAD DISK ASSEMBLY (HDA)

The mechanical portion of a rigid, fixed disk drive. It usually includes
disks, heads, spindle motor, and actuator.

HEAD LOADING ZONE

The non-data area on the disk set aside for the controlled takeoff
and landing of the Winchester heads when the drive is turned on
and off. Dedicated annulus on each disk surface in which heads are
loaded, unloaded, or flying height is established. Head-disk contact
may occur in some instances; no data is recorded in this area.

HEAD POSITIONER

Also known as actuator, a mechanism that moves the arms that carry
read/write heads to the cylinder being accessed.

IIIII

INDEX

Similar to a directory, but used to establish a physical to logical
cross reference. Used to update the physical disk address (tracks
and sectors) of files and to expedite accesses.

INSIDE DIAMETER

The smallest radial position used for the recording and playback of
flux reversals on a magnetic disk surface.

INITIALIZATION

Applying input patterns or instructions to a device so that all
operational parameters are at a known value.

INPUT

Data entering the computer to be processed; also user commands.

INPUT/OUTPUT (I/O)

The process of entering data into or removing data from a computer
system or a peripheral device.

INTELLIGENT PERIPHERAL

A peripheral device that contains a processor or microprocessor to
enable it to interpret and execute commands.

INTERFACE

The data transmitters, data receivers, logic, and wiring that link one
piece of computer equipment to another, such as a disk drive to a
controller or a controller to a system bus.

INTERFACE STANDARD

The interface specifications agreed to by various manufacturers to
promote industry-wide interchangeability of products such as a disk
drive. Interface standards generally reduce product costs, allows
buyers to purchase from more than one source, and allow faster
market acceptance of new products.

INTERLEAVE

An ordering of physical sectors to be skipped between logical
sectors on your hard disk.

I/O PROCESSOR

Intelligent processor or controller that handles the input/output
operations of a computer.

INTERRUPT

A signal, usually from a subsystem to a central processing unit, to
signify that an operation has been completed or cannot be
completed.

JJJJJ

JUMPER

A small piece of plastic that slides over pairs of pins that protrude
from the circuit board on the hard drive to make an electrical
connection and activate a specific option.

KKKKK

KILOBYTE (KB)

A unit of measure of approximately 1,000 bytes. (However, because
computer memory is partitioned into sizes that are a power of two, a
kilobyte is really 1,024 bytes.)