GLOSSARY
GL – 5
R
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.
S
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.
SOFT ERROR
A data error which can be overcome by rereading the data or repositioning the head.
SOFT SECTORED
A technique where the controller determines the beginning of a sector by the reading
of format information from the disk. This is contrasted to hard sectoring where a
digital signal indicates the beginning of a sector on a track.
SOFTWARE
Applications programs, operating systems, and other programs (as opposed to
hardware).
SPINDLE
The rotating hub structure to which the disks are attached.
SPINDLE MOTOR
The motor that rotates the spindle and therefore the disks.
SPUTTERED MEDIA
Magnetic disk or tape that has the magnetic layer deposited by sputtering means.
STEPPER MOTOR
A motor that has known detent positions where the rotor will stop with the proper
control in some cases. The digitally controlled motor moves the head positioner from
track to track in small, step-like motions.
STORAGE CAPACITY
The amount of data that can be stored in a memory location, usually specified in
kilobytes for main memory and floppy drives and megabytes for mass storage devices.
STORAGE DENSITY
Usually refers to recording density (BPI, TPI, or a combination of the two.)
STORAGE LOCATION
A memory location, identified by an address where information may be read or
written.
STROBE OFFSET SIGNAL
A group of digital input signal levels which cause the read PLL and/or data decoder to
shift the decoding windows by fractional amounts. Often early/late are modified when
two signals are used.