GLOSSARY
CONTROLLER
A miniature CPU dedicated to controlling a peripheral device, such as a disk drive, tape drive, video display terminal, or printer. The controller executes commands from the central processing unit and reissues commands to the peripheral device.
CORRECTABLEERROR
An error that can be overcome by the use of Error Detection and Correction.
CYLINDER
On several disk surfaces sharing a common rotational axis, the aggregate of tracks at a given radial position. A set of disk tracks that are simultaneously under the set of read/write heads. This three-dimensional storage volume can be accessed after a single seek.
CYLINDERZERO
The outermost cylinder in a drive that can be used for data storage.
D
DATA
An ordered collection of information. In a specific case, it is the information processed by a computer.
DATASEPARATOR
An electronic circuit which decodes playback data and produces separate clock and data bits. Sometimes incorrectly used to denote data synchronizer.
DATASYNCHRONIZER
An electronic circuit producing a clock signal that is synchronous with the incoming data stream. This clock signal is then used to decode the recording code being used into user data.
DATATRANSFERRATE
In a disk or tape drive, the rate at which data is transferred to or from the storage media. It is usually given in thousands of bits per second (Kbit/second) or millions of bits per second (Mbit/second).
DEDICATEDLANDINGZONE
A designated radial zone on the disk where contact starting and stopping occur by design.
DEDICATEDSERVO
A servo scheme in which a prerecorded pattern on an otherwise unused disk surface provides position information to the servo circuitry by means of a head reading that surface.
DEFECT
A magnetic imperfection in a recording surface.
DEFECTMANAGEMENT
A general methodology of avoiding data errors on a recording surface by avoiding the use of known bad areas of media. Usually defective sectors or tracks are retired and data are written in alternate locations. Several algorithms are possible such as “sector slipping,” or “spare sector per track.”
DEFECTMAP
A list of defects that fall within a pass/fail criteria of a user. This list is usually used by an operating system or a disk drive controller for defect management.
DEFECTSKIPPING
A defect management scheme for avoiding surface defects. It has data written before and after the defect, instead of using alternate tracks or sectors to avoid use of the defective area.
DENSITY
Generally, recording density. See areal, bit, and storage density.
DCERASE
The method of erasing a track using a DC write/erase current through either a Read/Write or Erase head.
DIGITAL
Any system that processes digital binary signals (having only values of a 1 or 0; usually in bits and bytes) rather than analog signals (signals that can have many values)
DIGITALMAGNETICRECORDING
See magnetic recording.
DIRECTACCESS
Access directly to memory location. (See random access).
DIRECTMEMORYACCESS
A mean of data transfer between the device and host memory without processor intervention.
DIRECTORY
A listing of files maintained by the disk operation system (DOS) or a data base management system to enable a user to quickly access data files.
DISK
A flat, circular piece of metal (usually aluminum) or plastic (usually mylar) with a magnetic coating upon which information can be recorded. (See, for example, floppy disk or Winchester disk)
DISKDRIVEORDISKMEMORYDEVICE
The total electromechanical storage device containing disks and read/write heads, head positioning mechanism, drive motor, and electronics.
DISKPACK
A number of metal disks packaged in a canister for removal from the disk drive (predecessor of Winchester technology).
DISKOPERATINGSYSTEM(DOS)
The master computer system program that schedules tasks, allocates the computer system resources, controls accesses to mass storage devices, manages files, and so forth. Typical disk operating systems include CP/M, MS-DOS, and UNIX.
DISKSTORAGE
Auxiliary memory system containing disk drives.
DISKTRANSFERRATE
The rate that digital data is transferred from one point to another. Expressed in either bits/second or bytes/second.
DOUBLEFREQUENCYENCODING
Another name for FM encoding. This is because all possible data combinations will result in only two possible temporal displacements of adjacent data bits, specifically “1F” and 2F.”
E
EARLYWINDOW
A data window that has been intentionally shifted in time in an early direction.
EMBEDDEDSERVO
A servo technique used for track following. Position information is prerecorded between data areas in a track so that a data head, and proper additional circuitry, can determine the data head location with respect to the center position of the track (or cylinder) in question.
ERASE
A process by which a signal recorded on a medium is removed and the medium made ready for rerecording.
ERRORCORRECTIONCODE(ECC)
A mathematical algorithm that can detect and correct errors in a data field. This is accomplished with the aid of Check Bits added to the raw data.
ERRORFREE
A recording surface that has no defects.
ERRORRATE
The number of errors (type must be specified) that occur in a specified number of bits read.
ERRORRECOVERYPROCEDURE
The process that occurs in response to a data error. In a drive without ECC, this would include re-calibration and re-seeking to the specified track and rereading the specified data.
