GLOSSARY
GL – 4
L
LANDING ZONE OR LZONE
The cylinder number to where ParkHeads move the read/write heads.
LATE BIT
A bit that is in the late half of the data window.
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.”
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 10
6
.
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.
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.
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.
P
PARALLELISM
1. The condition of two planes or lines being parallel. Important in
disk drives because a lack of it in mechanical assemblies can result
in positioning inaccuracy. More precisely: planes-coplanar; lines-
colinear. 2. Is the local variation in disk thickness measured
independently of thickness itself. 3. The ability of a multiprocessor
computer to allocate more than one processor (CPU) to a computing
problem, where each CPU works on a separate problem or separate
segment of that problem. Also referred to as parallel processing.
PARITY
A simple method of data error detections that always makes numbers
either odd or even, using an extra bit in which the total number of
binary 1s (or 0s) in a byte is always odd or always even; thus, in an
odd parity scheme, every byte has eight bits of data and one parity
bit. If using odd parity and the number of 1 bits comprising the byte
of data is not odd, the ninth or parity bit is set to 1 to create the odd
parity. In this way, a byte of data can be checked for accurate
transmission by simply counting the bits for an odd parity indication.
If the count is ever even, an error is indicated.
PARTITION
A logical section of a disk drive, each of which becomes a logical
device with a drive letter.
PEAK SHIFT
The shifting in time of the zero-slope portion of a readback voltage
from the values contained in the write current waveform. Sometimes
incorrectly used to describe bit jitter.
PERIPHERAL EQUIPMENT
Auxiliary memory, displays, printers, and other equipment usually
attached to a computer system’s CPU by controllers and cables.
(They are often packaged together in a desktop computer.)
PHASE LOCKED LOOP (PLL)
A circuit whose output locks onto and tracks the frequency of an
input signal. Sometimes incorrectly called a data separator.
