Glossary
BPI – Abbreviation for bits per inch. A measure of how densely information is packed on a storage medium. Flux changes per inch is also a term commonly used in describing storage density on a magnetic surface.
BUFFER – An area of RAM reserved for temporary storage of data that is waiting to be sent to a device that is not yet ready to receive it. The data is usually on its way to or from the disk drive or some other peripheral device.
BUS – The part of a chip, circuit board, or interface designed to send and receive data.
BYTE – The basic unit of computer memory, large enough to hold one character of alphanumeric data. Comprised of eight bits. See also bit.
C
CACHE –
CAPACITY – The amount of information that can be stored on a disk drive. The data is stored in bytes, and capacity is usually expressed in megabytes.
CDB – Command Descriptor Block. The SCSI structure used to communicate requests from an initiator (system) to a target (drive).
CLEAN ROOM – An environmentally controlled
CLUSTER – A group of sectors on a disk drive that is addressed as one logical unit by the operating system.
CONTROLLER – Short form of disk controller. The chip or complete circuit that translates computer data and commands into a form suitable for use by the disk drive.
CONTROLLER CARD – An adapter holding the control electronics for one or more hard disks, usually installed in a slot in the computer.
CPU – Acronym for Central Processing Unit. The microprocessor chip that performs the bulk of data processing in a computer.
CRC – Acronym for Cyclic Redundancy Check. An error detection code that is recorded within each sector and is used to see whether parts of a string of data are missing or erroneous.
CYLINDER – On a disk drive that has more than one recording surface and heads that move to various tracks, the group of all tracks located at a given head position. The number of cylinders times the number of heads equals the number of tracks per drive.
D
DATA SEPARATOR – On a disk drive that stores data and timing information in an encoded form, the circuit that extracts the data from the combined data and clock signal.
DEDICATED SERVO – A surface separate from the surface used for data that contains only disk timing and positioning information and contains no data.
DEFECT MANAGEMENT – A method that is implemented to ensure long term data integrity. Defect management eliminates the need for user defect maps. This is accomplished by scanning the disk drives at the factory for defective sectors. Defective sectors are deallocated prior to shipment. In addition, during regular use, the drive continues to scan and compensate for any new defective sectors on the disk.
DISK – In general, any