Maxtor ATLAS 10K IV User Manual page 246

Glossary
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.
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.
G-8 Maxtor Atlas 10K IV
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.
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.
RECONNECT – The act of reviving a nexus to
continue an I/O process. An initiator
reconnects to a target using the SELECTION
and MESSAGE OUT phases after winning
arbitration. The target reconnects to the
initiator using RESELECTION and
MESSAGE IN phases after winning
arbitration.
RECONNECTION – The state which results
from a reconnect. It exists from the assertion of
BSY in the SELECTION or RESELECTION
phase and lasts until the next BUS FREE phase.