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GLOSSARY
GL – 3
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.
G
GIGABYTE (GB)
One billion bytes (one thousand megabytes) or 10
9
.
H
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.
I
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.
J
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.
K
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.)
L
LANDING ZONE OR LZONE
The cylinder number to where ParkHeads move the read/write heads.
LATE BIT
A bit that is in the late half of the data window.
LATE WINDOW
A data window that has been shifted in a late direction to facilitate data recovery.
LATENCY
A delay encountered in a computer when waiting for a specific response. In a disk
drive there is both seek latency and rotational latency. The time required for the
addressed sector to arrive under the head after the head is positioned over the correct
track. It is a result of the disk’s rotational speed and must be considered in determining
the disk drive’s total access time.
LOGIC
Electronic circuitry that switches on and off (“1” and “0”) to perform functions.