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GLOSSARY
GL – 5
late window
A data window that has been shifted in a late direction to
facilitate data recovery.
latency
A delay encountered in a computer when waiting for a
specific response. In a disk drive there is both seek
latency and rotational latency. The time required for the
addressed sector to arrive under the head after the head
is positioned over the correct track. It is a result of the
disk’s rotational speed and must be considered in
determining the disk drive’s total access time.
logic
Electronic circuitry that switches on and off (“1” and “0”)
to perform functions.
logical address
A storage location address that may not relate directly to
a physical location. Usually used to request information
from a controller, which performs a logical to physical
address conversion, and in turn, retrieves the data from a
physical location in the mass storage peripheral.
logical block addressing
Defines the addressing of the device by the linear
mapping of sectors.
logical sector
The lowest unit of space that DOS can access through a
device driver; one or more physical sectors.
low frequency
The lowest recording frequency used in a particular
magnetic recording device. With FM or MFM channel
codes, this frequency is also called “IF.”
MM
MM
M
main memory
Random-access memory (RAM) used by the central
processing unit (CPU) for storing program instructions
and data currently being processed by those instructions.
(See also random access memory.)
mass storage
Auxiliary memory used in conjunctions with main
memory; generally having a large, on-line storage
capacity.
megabyte (MB)
A unit of measure approximately one million bytes
(actually 1,048,576 bytes) or 10E6.
memory
Any device or storage system capable of storing and
retrieving information. (See also storage definitions.)
microcomputer
A computer whose central processing unit is a
microprocessor. It is usually, but not necessarily, desktop
size.
microprocessor
A central processing unit (CPU) manufactured as a chip or
a small number of chips.
missing pulse
A term used in surface certification. It is when a
prerecorded signal is reduced in amplitude by a certain
specified percentage.
modified frequency modulation (MFM)
A method of encoding digital data signals for recording
on magnetic media. Also called “three frequency
recording.” Recording code that only uses synchronizing
clock pulse if data bits are not present. Doubles the lineal
bit density without increasing the lineal flux reversal
density, compared to Frequency Modulation.
modified modified frequency modulation (MMFM)
A recording code similar to MFM that has a longer run
length limited distance.
modulation
1. Readback voltage fluctuation usually related to the
rotational period of a disk. 2. A recording code, such as
FM, MFM, or RLL, to translate between flux reversals
and bits or bytes.
NN
NN
N
non-return to zero
A form of data encoding that is not self-clocking, in other
words, it needs to be provided with an external bit cell
clock signal. Generally used in higher-performance disk
drives.
OO
OO
O
off-line
processing or peripheral operations performed while
disconnected from the system CPU via the system bus.
on-line
processing or peripheral operations performed while
disconnected from the system CPU via the system bus.
open loop servo
A head positioning system that does not use positional
information to verify and correct the radial location of the
head relative to the track. This is usually achieved by use
of a stepper motor which has predetermined stopping
point that corresponds to track locations.
operating system
A software program that organizes the actions of the
parts of the computer and its peripheral devices. (See
disk operating system.)
outside diameter
The largest radius recording track on a disk.
overwrite
A test that measures the residual 1F recorded frequency
on a track after being overwritten by a 2F signal.
Variations of the test exist.