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Term
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Description
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Data
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An ordered collection of information. In a specific case, it is the information processed by a computer.
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Data Reliability
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Average data error rate allowed with all error recovery features activated.
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Data Seperator
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An electronic circuit which decodes playback data and produces separate clock and data bits. Sometimes incorrectly used to denote data synchronizer.
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Data Synchronizer
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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.
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Data Transfer Rate
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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).
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DC Erase
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The method of erasing a track using a DC write/erase current through either a Read/Write or Erase head.
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Dedicated Landing Zone
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A designated radial zone on the disk where contact starting and stopping occur by design.
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Dedicated Servo
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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.
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Defect
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A magnetic imperfection in a recording surface.
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Defect Map
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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.
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Defect Management
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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".
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Defect Skipping
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A defect management scheme for avoiding surface defects. In this case, data are written before and after the defect, instead of using alternate tracks or sectors to avoid the use of the defective area.
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Density
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Generally, recording density.
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Digital
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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/infinite values).
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Digital Magnetic Recording
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Also known as magnetic recording.
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Digital Signal Processor (DSP)
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Direct Access
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Access directly to memory location. (Applies to Random Access Memory).
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Direct Memory Access
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A mean of data transfer between the device and host memory without processor intervention. There are two DMA modes, Single and Multi-Word. Single word is slower than PIO mode, so, it is rarely used.
Multi Word DMA is used in EISA, VLB, and PCI equipped systems, which are capable of the very fast transfer rates, utilizing cycle times of 480ns or faster.
The current ATA specification limit is 150ns, virtually eliminating the CPU from the transfer process.
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Directory
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A listing of files maintained by the disk operation system or a data base management system to enable a user to quickly access data files.
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Disk
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A flat, circular piece of metal (usually aluminum) or plastic (usually mylar) with a magnetic coating upon which information can be recorded.
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