EXTRAPULSE
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.
F
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.
FILEALLOCATIONTABLE(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.
FLUXCHANGESPERINCH
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.
FORMATTEDCAPACITY
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.
FREQUENCYMODULATION
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.
FREQUENCYRESPONSE
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 109.
H
HARDERROR
An error that is not able to be overcome by repeated readings and repositioning means.
HARDSECTORED
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.
HEADCRASH
The inadvertent touching of a disk by a head flying over the disk (may destroy a portion of the media and/or the head).
GLOSSARY
HEADDISKASSEMBLY(HDA)
The mechanical portion of a rigid, fixed disk drive. It usually includes disks, heads, spindle motor, and actuator.
HEADLOADINGZONE
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.
HEADPOSITIONER
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.
INSIDEDIAMETER
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.
INTELLIGENTPERIPHERAL
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.
INTERFACESTANDARD
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/OPROCESSOR
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.)
