Seagate DiamondMax 17 Manual page 59

PLATTER – An disk made of metal (or other rigid
material) that is mounted inside a fixed disk drive. Most
drives use more than one platter mounted on a single spindle
(shaft) to provide more data storage surfaces in a small
package. The platter is coated with a magnetic material that
is used to store data as transitions of magnetic polarity.
POH – Acronym for 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 MTBF.
POSITIONER – See actuator.
R
RAM – Acronym for random access memory . An integrated
circuit memory chip which allows information to be stored
and retrieved by a microprocessor or controller. The
information may be stored and retrieved in any order
desired, and the address of one storage location is as readily
accessible as any other.
RAM DISK – A "phantom disk drive" for which a
section of system memory (RAM) is set aside to hold data,
just as if it were a number of disk sectors. The access to this
data is extremely fast but is lost when the system is reset or
turned off.
READ AFTER WRITE – A mode of operation that has
the computer read back each sector on the disk, checking
that the data read back is the same as recorded. This slows
disk operations, but raises reliability.
READ VERIFY – A disk mode where the disk reads in
data to the controller, but the controller only checks for
errors and 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.
RLL – Run Length Limited. A method used on some hard
disks to encode data into magnetic pulses. RLL requires
more processing, but stores almost 50% more data per disk
than the MFM method.
ROM – Acronym for read only memory. Usually in the form
of an ROM in the controller that contains programs that can
be accessed and read but not modified by the system.
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 the average, it is half of the
time needed for a full rotation (about 8 ms.).
SATA - Acronym for Serial ATA.
SCSI – Acronym for Small Computer System Interface, an
American National Standards Institute (ANSI) version of
Shugart Associates' SASI interface between the computer
and controller. SCSI has grown in popularity and is one of
the most flexible and intelligent interfaces available.
SECTOR – A section of space along a track on the disk, or
the data that is stored in that section. Hard disks most often
have sectors that are 512 data bytes long plus several bytes
overhead for error correcting codes. Each sector is preceded
by ID data known as a header, which cannot be overwritten.
SEEK – A movement of the disk read/write head in or out
to a specific 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 when a track to
track movement of the head stops, and when the residual
vibration and movement dies down to a level sufficient for
reliable reading or writing.
SHOCK RATING – A rating (expressed in Gs) of how
much shock a disk drive can sustain without damage.
SOFT ERROR – An error in reading data from the disk
that does not recur if the same data is reread. Often caused
by power fluctuations or noise spikes.
SOFT SECTORED – Disks that mark the beginning of
each sector of data within a track by a magnetic pattern.
Maxtor DiamondMax 17 80-160GB Serial ATA Hard Disk Drive
Glossary
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