GLOSSARY
L
LANDINGZONEORLZONE
The cylinder number to where ParkHeads move the read/write heads.
LATEBIT
A bit that is in the late half of the data window.
LATEWINDOW
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.
LOGICALADDRESS
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.
LOGICALBLOCKADDRESSING
Defines the addressing of the device by the linear mapping of sectors.
LOGICALSECTOR
The lowest unit of space that DOS can access through a device driver; one or more physical sectors.
LOWFREQUENCY
The lowest recording frequency used in a particular magnetic recording device. With FM or MFM channel codes, this frequency is also called “IF.”
M
MAINMEMORY
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.)
MASSSTORAGE
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 106.
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.
MISSINGPULSE
A term used in surface certification. It is when a prerecorded signal is reduced in amplitude by a certain specified percentage.
MODIFIEDFREQUENCYMODULATION(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.
MODIFIEDMODIFIEDFREQUENCYMODULATION(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-RETURNTOZERO
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.
OPENLOOPSERVO
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.
OPERATINGSYSTEM
A software program that organizes the actions of the parts of the computer and its peripheral devices. (See disk operating system.)
OUTSIDEDIAMETER
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.
PEAKSHIFT
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.
PERIPHERALEQUIPMENT
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.)
PHASELOCKEDLOOP(PLL)
A circuit whose output locks onto and tracks the frequency of an input signal. Sometimes incorrectly called a data separator.
