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
Loading...