Glossary
Quantum Fireball Plus LM 10.2/15.0/20.5/30.0 GB AT G-7
RLL – Run Length Limited. A method used
on some hard disks to encode data into
magnetic pulses. RLL requires more
processing, but stores almost 50% more data
per disk than the MFM method.
ROM – Acronym for read only memory.
Usually in the form of an ROM in the
controller that contains programs that can
be accessed and read but not modified by the
system.
ROTARY ACTUATOR – The rotary
actuator replaces the stepper motor used in
the past by many hard disk manufacturers.
The rotary actuator is perfectly balanced and
rotates around a single pivot point. It allows
closed-loop feedback positioning of the
heads, which is more accurate than stepper
motors.
ROTATIONAL LATENCY – The delay
between when the controller starts looking
for a specific block of data on a track and
when that block rotates around to where it
can be read by the read/write head. On the
average, it is half of the time needed for a full
rotation (about 8 ms.).
S
SS
S
SCSI – Acronym for Small Computer
System Interface, an American National
Standards Institute (ANSI) version of
Shugart Associates' SASI interface between
the computer and controller. SCSI has
grown in popularity and is one of the most
flexible and intelligent interfaces available.
SECTOR – A section of space along a track
on the disk, or the data that is stored in that
section. Hard disks most often have sectors
that are 512 data bytes long plus several
bytes overhead for error correcting codes.
Each sector is preceded by ID data known as
a header, which cannot be overwritten.
SEEK – A movement of the disk read/write
head in or out to a specific track.
SERVO DATA – Magnetic markings written
on the media that guide the read/write heads
to the proper position.
SERVO SURFACE – A separate surface
containing only positioning and disk timing
information but no data.
SETTLE TIME – The interval between when
a track to track movement of the head stops,
and when the residual vibration and
movement dies down to a level sufficient for
reliable reading or writing.
SHOCK RATING – A rating (expressed in
Gs) of how much shock a disk drive can
sustain without damage.
SOFT ERROR – An error in reading data
from the disk that does not recur if the same
data is reread. Often caused by power
fluctuations or noise spikes.
SOFT SECTORED – Disks that mark the
beginning of each sector of data within a
track by a magnetic pattern.
SPINDLE – The center shaft of the disk
upon which the drive’s platters are mounted.
SPUTTER – A type of coating process used
to apply the magnetic coating to some
high-performance disks. In sputtering, the
disks are placed in a vacuum chamber and
the coating is vaporized and deposited on
the disks. The resulting surface is hard,
smooth, and capable of storing data at high
density. Quantum disk drives use sputtered
thin film disks.
STEPPER – A type of motor that moves in
discrete amounts for each input electrical
pulse. Stepper motors used to be widely used
for read/write head positioner, since they
can be geared to move the head one track per
step. Stepper motors are not as fast or
reliable as the rotary voice coil actuators
which Quantum disk drives use.
SUBSTRATE – The material the disk platter
is made of beneath the magnetic coating.
Hard disks are generally made of aluminum
or magnesium alloy (or glass, for optical
disks) while the substrate of floppies is
usually mylar.
SURFACE – The top or bottom side of the
platter which is coated with the magnetic
material for recording data. On some drives
one surface may be reserved for positioning
information.