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Glossary
PARKING ZONE – A position in a non-data
area on a disk platter reserved for resting the
heads when power is off. Using this area
prevents the heads from touching the surface in
data areas upon power down, adding to the data
integrity and reliability of the disk drive. The
parking zone is most often inside the disk's
inner-most cylinder.
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.
PHYSICAL FORMAT – The actual physical
layout of cylinders, tracks, and sectors on a
disk drive.
PHYSICAL SECTOR –See sector, data.
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.
PREFETCH –The technique of buffering data
into cache RAM by reading subsequent blocks
in advance to anticipate the next request for
data. Prefetch speeds up disk accesses to
sequential blocks of data.
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.
G-8
Maxtor Atlas 15K
Q
QUEUE – A prioritized list or set of processes.
A queue may be a FIFO (first-in, first-out),
LIFO (last-in, first -out) or a random-access
entity.
QUEUE TAG – The value associated with an I/
O process that uniquely identifies it from other
queued I/O processes in the logical unit from
the same initiator.
QUEUED I/O PROCESS – An I/O process that
is in the command queue.
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.
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 – The function of detecting, processing
and transmitting data that has been recorded
(written) on a magnetic disk or some other
media.
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.
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