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GLOSSARY

GL – 5

PHASE MARGIN

Measure in degrees of the amount of difference between
excursions from the window center where flux reversals can occur
and the edge of the data window. Similar to window margin.

PHYSICAL SECTOR

The smallest grouping of data on the hard disk; always 512 bytes.

PIO

Programmable Input Output. A means of accessing device registers.
Also describes one form of data transfers. PIO data transfers are
performed by the host processor using PIO register accesses to the
data register.

PLATED THIN FILM MEDIA

Magnetic disk memory media having its surface plated with a thin
coating of a metallic alloy instead of being coated with oxide.

PROCESSING

The process of the computer handling, manipulating and modifying
data such as arithmetic calculation, file lookup and updating, and
word pressing.

PULSE CROWDING

Modification of playback amplitude due to super-positioning of
adjacent flux reversal fields being sensed by the read/write gap.

PULSE DETECT

A digital pulse train in which each leading edge or each edge
corresponds to a magnetic transition read from the disk. If transition
qualification circuitry exists in the drive, this signal is the output of
same. Also known as transition detect.

RRRRR

RANDOM ACCESS MEMORY (RAM)

Memory designed so that any storage location can be accessed
randomly, directly and individually. This is contrasted to sequential
access devices such as tape drives.

READ

To access a storage location and obtain previously recorded data.
To sense the presence of flux reversals on magnetic media. Usually
implemented such that a dynamic flux amplitude will cause a
proportional electrical output from the transducer.

READ GATE SIGNAL

A digital input signal which causes the drive circuitry to recover
data.

READ ONLY MEMORY (ROM)

A form of memory which cannot be changed in formal operational
modes. Many different types are available. RAM is used for
permanent information storage. Computer control programs are
often stored in ROM applications.

READ/WRITE HEAD

The recording element which writes data to the magnetic media and
reads recorded data from the media.

RE-CALIBRATE

The action of moving the head of a disk drive to cylinder zero.

RECOVERABLE ERROR

A read error, transient or otherwise, falling within the capability of
an ECC mechanism to correct, or able to overcome by rereading the
data in question.

ROTATIONAL LATENCY

The amount of delay in obtaining information from a disk drive
attributable to the rotation of the disk.

RUN-LENGTH LIMITED

An encoding process that repositions data bits and limits the length
of zero bits in order to compress information being stored on disks.

RUN-LENGTH LIMITED ENCODING

A recording code. Sometimes meant to denote “2.7 RLL” which can
signify 1.5 times the bits as MFM, given the same number of flux
reversals in a given lineal distance.

SSSSS

SECTOR

A logical segment of information on a particular track. The smallest
addressable unit of storage on a disk. Tracks are made of sectors.

SECTOR PULSE SIGNAL

A digital signal pulse present in hard sectored drives which
indicates the beginning of a sector. Embedded servo pattern or
other prerecorded information may be present on the disk when
sector is active.

SEEK

A random access operation by the disk drive. The act of moving a set
of read/write heads so that one of them is over the desired cylinder.
The actuator or positioner moves the heads to the cylinder
containing the desired track and sector.

SEEK COMPLETE SIGNAL

A digital signal level which indicates that the positioner is not
moving and is located over a cylinder or offset position.

SEEK TIME

The amount of time between when a step pulse or seek command is
issued until the head settles onto the desired cylinder. Sometimes is
measured without settling times.

SEQUENTIAL ACCESS

The writing or reading of data in a sequential order such as reading
data blocks stored one after the other on magnetic tape. This is
contrasted to random access of information.

SERVO BURST

A momentary servo pattern used in embedded servo control systems
usually positioned between sectors or at the end of a track.

SERVO CONTROL

A technique by which the speed or position of a moving device is
forced into conformity with a desired or standard speed or position.

SERVO HEAD

A magnetic head designed specifically for accurately reading servo
data.

SERVO PATTERN

A readback signal that indicates the position of a head relative to a
track.

SERVO SURFACE

A recording surface in a multi-surface disk drive that only contains
control information which provides timing, head position, and track-
following information for the data surfaces.

SERVO SYSTEM

An automatic system for maintaining the read/write head on track;
can be either “open loop,” “quasi-closed loop,” or “closed loop.”

SERVO TRACK

A track on a servo surface. The prerecorded reference track on the
dedicated servo surface of a disk drive. All data track positions are
compared to their corresponding servo track to determine “off
track”/”on track” position.

SETTLING TIME

The time it takes a head to stop vibrating, within specified limits,
after it reaches the desired cylinder.

SILICON

Semiconductor material generally used to manufacture
microprocessors and other integrated circuit chips.

SMALL COMPUTER SYSTEM INTERFACE (SCSI)

An intelligent interface that incorporates controller functions
directly into the drive.

S.M.A.R.T. CAPABILITY

Self-Monitoring Analysis and Reporting Technology. Prediction of
device degradation and/or faults.