Maxtor Atlas SCSI Drive 15K II, Руководство по эксплуатации продукта

Страница: 247 / 260

Glossary
Maxtor Atlas 15K G-7
MAGNETO-RESISTIVE – A unique
characteristic of some metals, which, when
combined, yields a variable electrical resistance
to varying magnetic fluxes. The resistance varies
directly with the strength of the flux, field, not
simply to a change in flux as with magneto-
inductance.
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 1,024,000 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.
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.
N
.NANOSECOND (ns) – One billionth of a
second (0.000 000 001 second or 10-9 second).
NEXUS – A relationship between two devices
that begins with the establishment of an initial
connection and ends with the completion of an I/
O process. A nexus relationship is further
defined by the letters I (initiator), T (target), L
(logical unit), R (target routine), x (either L or
R), Q (queue tag), and x_y (either an x or a Q)
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 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
PARITY – An error checking technique wherein
the sum of the bits in a data byte is used to set or
reset an extra parity bit, depending on whether
the sum is an odd or an even number. A second
parity check after the data is transferred to a new
location checks that the new parity bit matches
the transferred bit. Parity checking can only
detect an odd number of bit errors (1,3,5, etc.).
Parity is defined as odd or even, depending on
which condition (odd or even) is used to set the
parity bit.