Octek all models GLOSSARY

GLOSSARY

A

ACCESS – (v) Read, write, or update information

stored on a disk or other medium. (n) The
operation of reading, writing, or updating stored
information.

ACCESS TIME – The interval between the time a

request is made by the system and the time the
data is available from the drive. Includes the seek
time, rotational latency, and command processing
overhead time. (See also seek , rotational latency ,
and overhead .)

ACTUATOR – Also known as the positioner . The

internal mechanism that moves the read/write
head to the proper track. The Quantum actuator
consists of a rotor connected to head mounting
arms that position the heads over the desired
cylinder. Also known as rotary actuator.

AIRLOCK – A patented Quantum feature that

ensures durable and reliable data storage. Upon
removal of power from the drive for any reason,
the read/write heads automatically park and lock
in a non data area called the landing zone.
Airlock allows the drive to withstand high levels
of non-operating shock. When power is applied to
the drive, airflow created from the spinning disks
causes the Airlock arm to swing back and unlock
the actuator, allowing the heads to move from the
landing zone. Upon power down, the Airlock
swings back to the locked position, locking the
heads in the landing zone. A park utility is not
required to park the heads on drives equipped
with Airlock (all Quantum drives).

ALLOCATION – The process of assigning

particular areas of the disk to specific data or
instructions. An allocation unit is a group of
sectors on the disk reserved for specified
information. On hard disks for small computer
systems, the allocation unit is usually in the form
of a sector, block, or cluster. (See also allocation

unit .)

ALLOCATION UNIT – An allocation unit, also

known as a cluster , is a group of sectors on the
disk that can be reserved for the use of a
particular file.

ASIC – Acronym for Application Specific

Integrated Circuit .

AVERAGE SEEK TIME – The average time it takes

for the read/write head to move to a specific
location. Calculated by dividing the time it takes
to complete a large number of random seeks by
the number of seeks performed.

B

BACKUP – A copy of a file, directory, or volume

on a separate storage device from the original, for
the purpose of retrieval in case the original is
accidentally erased, damaged, or destroyed.

BAD BLOCK – A block (usually the size of a

sector) that cannot reliably hold data due to a
physical flaw or damaged format markings.

BAD TRACK TABLE – A label affixed to the

casing of a hard disk drive stating which tracks
are flawed and cannot hold data. This list is typed
into the low-level formatting program when the
drive is installed. Quantum users can ignore bad
track tables since Quantum’s built-in defect­management protections compensate for these
flaws automatically.

BEZEL – A plastic panel that extends the face of

a drive so that it covers a computer’s drive bay
opening. The bezel usually contains a drive­activity LED. Also known as the faceplate .

BIT – Abbreviation for binary digit. A binary digit

may have one of two values—1 or 0. This
contrasts with a decimal digit, which may have a
value from 0 to 9. A bit is one of the logic 1or
logic 0 binary settings that make up a byte of
data. (See also byte .)

BLOCK – In UNIX workstation environments, the

smallest contiguous area that can be allocated for
the storage of data. UNIX blocks are generally 8
Kbytes (16 sectors) in size. In DOS environments,
the block is referred to as a cluster. (Note: This
usage of the term block at the operating system
level is different from its meaning in relation to
the physical configuration of the hard drive. See

sector for comparison.)

Viking 2.27/4.55S G-1

Glossary

BPI – Bits Per Inch. A measure of how densely

information is packed on a storage medium. (See
also FCI .)

BUFFER – An area of RAM reserved for

temporary storage of data that is waiting to be
sent to a device that is not yet ready to receive it.
The data is usually on its way to or from the hard
disk drive or some other peripheral device.

BUS – The part of a chip, circuit board, or

interface designed to send and receive data.

BYTE – The basic unit of computer memory, large

enough to hold one character of alphanumeric
data. Comprised of eight bits. (See also bit .)

C

CACHE – Specialized High-speed RAM used to

optimize data transfers between system elements
with different performance characteristics, e.g.,
disk to main memory or main memory to CPU.

CAPACITY – The amount of information that can

be stored on a hard drive. Also known as storage
capacity. (See also formatted capacity .)

CLEAN ROOM – An environmentally controlled

dust-free assembly or repair facility in which
hard disk drives are assembled or can be opened
for internal servicing.

CLUSTER – In DOS environments, the smallest

contiguous area that can be allocated for the
storage of data. DOS clusters are usually 2 Kbytes
(4 sectors) in size.

CONTROLLER – The chip or circuit that translates

computer data and commands into a form
suitable for use by the hard drive. Also known as
disk controller.

CONTROLLER CARD – An adapter containing the

control electronics for one or more hard disks.
Usually installed in a slot in the computer.

CPU – Central Processing Unit. The

microprocessor chip that performs the bulk of
data processing in a computer.

CRC – Cyclic Redundancy Check. An error

detection procedure that identifies incomplete or
faulty data in each sector.

D

DATA SEPARATOR – The circuit that extracts

data from timing information on drives that store
a combined data and clock signal.

DEDICATED SERVO – A positioning mechanism

using a dedicated surface of the disk that contains
timing and positioning information only, as
compared to surfaces that are also used for data.
(See also embedded servo .)

DEFECT MANAGEMENT – A technique ensuring

long-term data integrity. Consists of scanning
disk drives both at the factory and during regular
use, de-allocating defective sectors before
purchase and compensating for new defective
sectors afterward.

DISK – In general, any circular-shaped data-

storage medium that stores data on the flat
surface of the platter. The most common type of
disk is the magnetic disk, which stores data as
magnetic patterns in a metal or metal-oxide
coating. Magnetic disks come in two forms:
floppy and hard. Optical recording is a newer disk
technology that gives higher capacity storage but
at slower access times.

DISK CONTROLLER – A plug-in board, or

embedded circuitry on the drive, that passes
information to and from the disk. The Quantum
hard disk drives all have controllers embedded on
the drive printed-circuit board. (See also

controller .)

DMA – Direct Memory Access. A process for

transferring data directly to and from main
memory, without passing through the CPU. DMA
improves the speed and efficiency by allowing
the system to continue processing even while
new data is being retrieved.

DOS – Disk Operating System. The most common

operating system used in IBM PCs. Manages all ac­cess to data on the disk.

DRIVE – Short form of disk drive .
DRIVE GEOMETRY – The functional dimensions

of a drive, including the number of heads,
cylinders, and sectors per track. (See also logical

format .)

CYLINDER – When disks are placed directly

above one another along the shaft, the circular,
vertical “slice” consisting of all the tracks located
in a particular position.

G-2 Viking 2.27/4.55S

Glossary

E

ECC – Error Correction Code. The incorporation

of extra parity bits in transmitted data in order to
detect errors that can be corrected by the
controller.

EMBEDDED SERVO – A timing or location signal

placed on tracks that store data. These signals
allow the actuator to fine-tune the position of the
read/write heads.

ENCODING – The conversion of data into a

pattern of On/Off or 1/0 signals prior to being
written on the disk surface. (See also RLL and

MFM .)

EPROM – Erasable Programmable Read-Only

Memory. An integrated circuit memory chip that
can store programs and data in a non-volatile
state. These devices can be erased by ultraviolet
light and reprogrammed with new data.

EXTERNAL DRIVE – A drive mounted in an

enclosure separate from the computer system
enclosure, with its own power supply and fan,
and connected to the system by a cable.

F

FCI – Flux Changes per Inch. The number of

magnetic field patterns that can be stored on a
given area of disk surface, used as a measure of
data density. (See also BPI .)

FILE SERVER – A computer that provides

network stations with controlled access to
shareable resources. The network operating
system is loaded on the file server, and most
shareable devices (disk subsystems, printers) are
attached to it. The file server controls system
security and monitors station-to-station
communications. A dedicated file server can be
used only as a file server while it is on the
network. A non dedicated file server can be used
simultaneously as a file server and a workstation.

FIRMWARE – Permanent instructions and data

programmed directly into the circuitry of read­only memory for controlling the operation of the
computer. Distinct from software, which can be
altered by programmers.

FLUX DENSITY – The number of magnetic field

patterns that can be stored in a given length of
disk surface. The number is usually stated as flux
changes per inch (FCI), with typical values in the
thousands. (See also FCI .)

FLYING HEIGHT – The distance between the

read/write head and the disk surface, made up of
a cushion of air that keeps the two objects from
touching. Smaller flying heights permit denser
data storage but require more precise mechanical
designs. Also known as fly height.

FORMAT – To write a magnetic track pattern

onto a disk surface, specifying the locations of
the tracks and sectors. This information must
exist on a disk before it can store data.

FORMATTED CAPACITY – The amount of room

left to store data on a disk after writing sector
headers, boundary definitions, and timing
information during a format operation. The size
of a Quantum drive is always expressed in
formatted capacity, accurately reflecting the
usable space required.

FORM FACTOR – The industry standard that

defines the physical, external dimensions of a
particular device. For example, most Quantum
hard disk drives use a 3 1/2-inch form factor.

G

GIGABYTE (GB) – One billion bytes (one

thousand megabytes).

GUIDE RAILS – Plastic strips attached to the sides

of a hard disk drive in an IBM PC/AT or
compatible computer so that the drive easily
slides into place.

H

HALF-HEIGHT – Standard drive size equivalent

to half the vertical space of a 5 1/4-inch drive.

HARD DISK – A type of storage medium that

retains data as magnetic patterns on a rigid disk,
usually made of an iron oxide or alloy over a
magnesium or aluminum platter. Because hard
disks spin more rapidly than floppy disks, and the
head flies closer to the disk, hard disks can
transfer data faster and store more in the same
volume.

HARD ERROR – A data error that persists when

the disk is re-read, usually caused by defects in
the physical surface.

HARD-SECTORED – The most common method

of indicating the start of each sector on a disk,
based on information located in the embedded

Viking 2.27/4.55S G-3

Glossary

servo. This method is more precise than soft­sectored techniques and results in lower
overhead. (See also soft-sectored .)

HEAD – The tiny electromagnetic coil and metal

pole used to create and read back magnetic
patterns on the disk. Also known as read/write
head.

HEAD CRASH – Damage to the read/write head,

usually caused by sudden contact with the disk
surface. Head crash can also be caused by dust
and other particles.

HIGH-CAPACITY DRIVE – By industry

conventions typically a drive of 100 megabytes
or more.

HIGH-LEVEL FORMATTING – Formatting

performed by the operating system to create the
root directory, file allocation tables and other
basic configurations. (See also low-level

formatting .)

HOME – Reference track used for recalibration of

the actuator. Usually the outermost track (track

0).

HOST ADAPTER – A plug-in board that acts as

the interface between a computer system bus and
the disk drive.

by, and then the next is read. It would take three
revolutions of the disk to access a full track of
data. Quantum drives have an interleave of 1:1,
so a full track of data can be accessed within one
revolution of the disk, thus offering the highest
data throughput possible.

INTERNAL DRIVE – A drive mounted inside one
of a computer’s drive bays, or a hard disk on a
card installed in one of the computer’s expansion
slots.

J

JUMPER – A tiny box that slips over two pins on
a circuit board, connecting the pins electrically.
Some board manufacturers use Dual In-Line
Package (DIP) switches instead of jumpers.

K

KILOBYTE (K) – A unit of measure consisting of
1,024 (210) bytes.

L

LANDING ZONE – A non-data area on the disk’s
inner cylinder where the heads can rest when the
power is off.

I

INITIALIZATION – See
INTERFACE – A hardware or software protocol,

(contained in the electronics of the disk controller
and disk drive) that manages the exchange of
data between the drive and computer. The most
common interfaces for small computer systems
are AT (also known as IDE) and SCSI.

INTERLEAVE – The arrangement of sectors on a
track. The Interleave Factor is the number of
sectors that pass beneath the read/write heads
before the next sector arrives. For example, a 3:1
interleave factor means that the heads read a
sector, then let two pass by before reading
another, requiring three full revolutions of the
disk to access the complete data track. Quantum
drives have an interleave factor of 1:1, allowing
the system to access a full track of data in a single
revolution.

INTERLEAVE FACTOR – The number of sectors
that pass beneath the read/write heads before the
next numbered sector arrives. When the
interleave factor is 3:1, a sector is read, two pass

low-level formatting.

LATENCY – The time during which the read/write
heads wait for the data to rotate into position
after the controller starts looking for a particular
data track. If a disk rotates at 3,600 rpm, the
maximum latency time is 16.4 milliseconds, and
the average latency time is 8.2 milliseconds.

LOOK AHEAD – The process of anticipating
events in order to speed up computer operations.
For example, the system can buffer data into
cache RAM by reading blocks in advance,
preparing the system for the next data request.

LOW-LEVEL FORMATTING – The process of
creating sectors on the disk surface so that the
operating system can access the required areas
for generating the file structure. Quantum drives
are shipped with the low-level formatting already
completed. Also known as initialization.

LOW PROFILE – Describes drives built to the
3 1/2-inch form factor, which are only 1 inch
high. The standard form factor drives are 1.625
inches high.

LPS – Low Profile Series.

G-4 Viking 2.27/4.55S

Glossary

M

MB – See megabyte.
MEDIA – The magnetic film that is deposited or

coated on an aluminum substrate which is very
flat and in the shape of a disk. The media is
overcoated with a lubricant to prevent damage to
the heads or media during head take off and
landing. The media is where the data is stored
inside the disk in the form of magnetic flux or
polarity changes.

MEGABYTE (MB) – A unit of measurement equal
to 1,000 kilobytes, or 1,000,000 bytes. (See also
kilobyte.)

MEGAHERTZ – A measurement of frequency in
millions of cycles per second.

MHz – See megahertz.
MICROPROCESSOR – The integrated circuit chip

that performs the bulk of data processing and
controls the operation of all of the parts of the
system. A disk drive also contains a
microprocessor to handle all of the internal
functions of the drive and to support the
embedded controller.

the space required for non-data information such
as location and timing. Disk overhead often
accounts for about ten percent of drive capacity.
Lower disk overhead yields greater disk capacity.

OVERWRITE – To write data on top of existing
data, erasing it.

OXIDE – A metal-oxygen compound. Most
magnetic coatings are combinations of iron or
other metal oxides, and the term has become a
general one for the magnetic coating on tape or
disk.

P

PARTITION – A portion of a hard disk dedicated
to a particular operating system and application
and accessed as a single logical volume.

PERFORMANCE – A measure of the speed of the
drive during normal operation. Factors affecting
performance are seek times, transfer rate and
command overhead.

PERIPHERAL – A device added to a system as an
enhancement to the basic CPU, such as a disk
drive, tape drive or printer.

MICROSECOND (µs) – One millionth of a second
(.000001 sec.).

MILLISECOND (ms) – One thousandth of a
second (.001 sec.).

MTBF – Mean Time Between Failure. Reliability
rating indicating the failure rate expected of a
product expressed in power on hours (POH). Since
manufacturers differ in the ways they determine
the MTBF, comparisons of products should
always take into account the MTBF calculation
method.

MTTR – Mean Time To Repair. The average time
it takes to repair a drive that has failed for some
reason. This only takes into consideration the
changing of the major sub-assemblies such as
circuit board or sealed housing. Component level
repair is not included in this number as this type
of repair is not performed in the field.

O

OVERHEAD – Command overhead refers to the
processing time required by the controller, host
adapter, or drive prior to the execution of a
command. Lower command overhead yields
higher drive performance. Disk overhead refers to

PHYSICAL FORMAT – The actual physical layout
of cylinders, tracks, and sectors on a disk drive.

PLATTER – Common term referring to the hard
disk.

POH – Power On Hours. The unit of measurement
for Mean Time Between Failure as expressed in
the number of hours that power is applied to the
device regardless of the amount of actual data
transfer usage. (See also MTBF.)

POSITIONER – See actuator
PRML – Partial-Response Maximum-Likelihood.

A sophisticated data-detection method that
improves data throughput and increases areal
density. PRML read channels are used in place of
peak-detection read channels.

R

RAM – Random Access Memory. An integrated
circuit memory chip that allows information to be
stored and retrieved by a microprocessor or
controller. The information may be stored and
retrieved in any order, and all storage locations
are equally accessible.

Viking 2.27/4.55S G-5

Glossary

RAM DISK – A “phantom” disk drive created by
setting aside a section of RAM as if it were a
group of regular sectors. Access to RAM disk data
is extremely fast, but is lost when the system is
reset or turned off.

READ AFTER WRITE – A mode of operation
requiring that the system read each sector after
data is written, checking that the data read back
is the same as the data recorded. This operation
lowers system speed but raises data reliability.

READ VERIFY – A data accuracy check
performed by having the disk read data to the
controller, which then checks for errors but does
not pass the data on to the system.

READ/WRITE HEAD – The tiny electromagnetic
coil and metal pole piece used to create and read
back the magnetic patterns (write or read
information) on the disk. Each side of each platter
has its own read/write head.

REMOVABLE DISK – Generally said of disk
drives where the disk itself is meant to be
removed, and in particular of hard disks using
disks mounted in cartridges. Their advantage is
that multiple disks can be used to increase the
amount of stored material, and that once
removed, the disk can be stored away to prevent
unauthorized use.

ROM – Read-Only Memory. Integrated circuit
memory chip containing programs that can be
accessed and read but can not be modified.

store information. On Macintosh and UNIX
drives, sectors are usually grouped into blocks or
logical blocks that function as the smallest data
unit permitted. Since these blocks are often
defined as a single sector the terms block and
sector are sometimes used interchangeably in this
context. (Note: The usage of the term block in
connection with the physical configuration of the
disk is different from its meaning at the system
level. See also block and cluster for comparison.)

SEEK – A movement of the disk read/write head
to a specific data 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 the arrival
of the read/write head at a specific track, and the
lessening of the residual movement to a level
sufficient for reliable reading or writing.

SHOCK RATING – A rating, expressed in “G’s”, of
how much shock a disk drive can sustain without
damage.

SOFT ERROR – A faulty data reading that does
not recur if the same data is reread from the disk,
or corrected by ECC. Usually caused by power
fluctuations or noise spikes.

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 average, it is half of the time
needed for a full rotation (about 8 ms.).

S

SCSI – Small Computer System Interface. An
interface designed for Apple Macintosh systems
and UNIX workstations.

SECTOR – On a PC hard drive, the minimum
segment of track length that can be assigned to

G-6 Viking 2.27/4.55S

SOFT-SECTORED – Old time-based method of
indicating the start of each sector on a disk. Soft­sectored drives require that location instructions
be located in the data fields. (See also hard-
sectored.)

SPINDLE – The drive’s center shaft, on which the
hard disks are mounted. A synchronized spindle
is a shaft that allows two disks to spin
simultaneously as a mirror image of each other,
permitting redundant storage of data.

SPUTTER – A special method of coating the disk
that results in a hard, smooth surface capable of
storing data at a high density. Quantum disk
drives use sputtered thin film disks.

STEPPER – A type of motor that moves in
discrete steps with each electrical pulse. Stepper
were originally the most common type of
actuator engine, since they can be geared to
advance a read/write head one track per step.
However, they are not as fast, reliable, or durable
as the voice coil actuators found in Quantum disk

Glossary

drives. (See also voice coil.)
SUBSTRATE – The material underneath the

magnetic coating of a disk. Common substrates
include aluminum or magnesium alloys for hard
drives, glass, for optical disks, and mylar for
floppy disks.

SURFACE – The top or bottom side of a disk,
which is coated with the magnetic material for
recording data. On some drives one surface may
be reserved for positioning information.

T

THIN FILM – A type of coating allowing very thin
layers of magnetic material, used on hard disks
and read/write heads. Hard disks with thin film
surfaces can store greater amounts of data.

TPI – Tracks Per Inch. The number of tracks
written within each inch of disk’s surface, used as
a measure of how closely the tracks are packed on
a disk surface. Also known as track density.

TRACK – One of the many concentric magnetic
circle patterns written on a disk surface as a guide
for storing and reading data. Also known as
channel.

V

VOICE COIL – A fast and reliable actuator motor
that works like a loud speaker, with the force of a
magnetic coil causing a proportionate movement
of the head. Voice coil actuators are more durable
than their stepper counterparts, since fewer parts
are subject to daily stress and wear. Voice coil
technology is used in all Quantum drives.

W

WEDGE SERVO – The position on every track
that contains data used by the closed loop
positioning control. This information is used to
fine tune the position of the read/write heads
exactly over the track center.

WINCHESTER DISKS – Former code name for an
early IBM hard disk model, sometimes still used
to refer to hard drives in general.

WRITE ONCE – An optical disk technology that
allows the drive to store and read back data, but
prevents the drive from erasing information once
it has been written.

TRACK DENSITY – How closely the tracks are
packed on a disk surface. The number is specified
as tracks per inch (TPI).

TRACK-TO-TRACK SEEK TIME – The time
required for the read/write heads to move to an
adjacent track.

TRANSFER RATE – The rate at which the disk
sends and receives data from the controller. The
sustained transfer rate includes the time required
for system processing, head switches and seeks,
and accurately reflects the drive’s true
performance. The burst mode transfer rate is a
much higher figure that refers only to the
movement of data directly into RAM.

U

UNFORMATTED CAPACITY – The total number
of usable bytes on a disk, including the space that
will be required to later to record location,
boundary definitions, and timing information.
(See formatted capacity for comparison.)

Viking 2.27/4.55S G-7

Glossary

G-8 Viking 2.27/4.55S