Glossary
BLOCK – In UNIX workstation environments, the smallest contiguous area that can be allocated for the storage of data. UNIX blocks are generally 8 Kbytes (16 sectors) in size. In DOS environments, the block is referred to as a cluster. (Note: This usage of the term block at the operating system level is different from its meaning in relation to the physical configuration of the hard drive. See sector for comparison.)
BPI – Bits Per Inch. A measure of how densely information is packed on a storage medium. (See also FCI.)
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 hard 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.)
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CACHE – Specialized
CAPACITY – The amount of information that can be stored on a hard drive. Also known as storage capacity. (See also formatted capacity.)
CLEAN ROOM – An environmentally controlled
CMOS – Acronym for complementary metal oxide semiconductor. A
COMMAND QUEUE – The queue used to store I/O processes.
CONNECT – The initiator function that selects a target to establish a nexus and to start an I/O process. The connection that results is an initial connection.
CONNECTION – An initial connection or reconnection that can occur only between one initiator and one target.
CONTINGENT ALLEGIANCE – A condition generated by a CHECK CONDITION or
COMMAND TERMINATED status during which execution of all tagged I/O processes (for the associated I_T_X nexus) are suspended until the condition is cleared. A target preserves an I_T_X nexus until it is cleared by a hard or soft reset, an abort message or another command for that I_T_X nexus. While the contingent allegiance condition exists, the target maintains sense data for the initiator.
CLUSTER – In DOS environments, the smallest contiguous area that can be allocated for the storage of data. DOS clusters are usually 2 Kbytes (4 sectors) in size.
CONTROLLER – The chip or circuit that translates computer data and commands into a form suitable for use by the hard drive. Also known as disk controller.
CONTROLLER CARD – An adapter containing the control electronics for one or more hard disks. Usually installed in a slot in the computer.
CPU – Central Processing Unit. The microprocessor chip that performs the bulk of data processing in a computer.
CRC – Cyclic Redundancy Check. An error detection procedure that identifies incomplete or faulty data in each sector.
CYLINDER – When disks are placed directly above one another along the shaft, the circular, vertical “slice” consisting of all the tracks located in a particular position.
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