IBM 3590 manual ERP. See error-recovery procedures

premounted tape cartridges or the manual loading of single tape cartridges.

CCR. Channel command retry.

channel. A device that connects the processing unit and main storage with the I/O control unit.

channel command. An instruction that directs a data channel, control unit, or device to perform an operation or set of operations.

command. A control signal that initiates an action or the beginning of a sequence of actions.

contingent allegiance. (1) A condition in which a drive owes a response to a specific channel path because of a unit check. (2) A condition generated by a check condition status during which a target preserves sense data.

control unit. A device that controls input and output operations of one or more devices.

control unit function. A device that contains the functional logic for controlling the input and output operations at one or more devices.

D

DASD. Direct-access storage device.

data. Any representations such as characters or analog quantities to which meaning is, or might be, assigned.

data base. A set of data, consisting of at least one file, that is sufficient for a given purpose or for a given data-processing system.

data compression. An algorithmic data-reduction technique that encodes data from the host and stores it in less space than unencoded data. The original data is recovered by an inverse process called decompression.

data-compression ratio. The number of host data bytes divided by the number of encoded bytes. It is variable depending on the characteristics of the data being processed. The more random the data stream, the lower the opportunity to achieve compression.

dataset. The major unit of data storage and retrieval, consisting of a collection of data in one of several prescribed arrangements and described by control information to which the system has access.

deferred unit check. A condition in which a drive returns a unit check indication for an event that occurred asynchronously with the channel commands. The deferred unit check may not refer to the command that receives the indication.

drive loaded. A condition of a tape drive in which a tape cartridge has been inserted in the drive, and the tape has been threaded to the beginning-of-tape position. Also known as a mount.

dump. To write the contents of storage, or of a part of storage, usually from an internal storage to a external medium, for a specific purpose such as to allow other use of storage, as a safeguard against faults or errors, or in connection with debugging.

E

effective data rate. The average number of bits, bytes, characters, or blocks per unit time transferred from a data source to a data sink and accepted as valid. The rate is expressed in bits, bytes, characters, or blocks per second, minute, or hour.

effective recording density. The number of user bytes per unit of length of the recording medium.

enable. To provide the means or opportunity. The modification of system, control unit, or device action through the change of a software module or a hardware switch (circuit jumper) position.

ERA. Error-recovery action performed by the host.

ERP. See error-recovery procedures.

1343590 Operator Guide