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Interleaved Data Transfers

IP.com Disclosure Number: IPCOM000082757D
Original Publication Date: 1975-Feb-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Baumer, LB: AUTHOR [+3]

Abstract

In a storage type of subsystem, diverse memory devices are employed. For example, tape units are relatively slow-access devices; while disk units are relatively rapid-access devices. In transferring data between a host (CPU) and a memory unit of the subsystem, it is desirable that most transfers occur between the disk unit and the host unit. Accordingly, staging operations are employed between the tape unit and the disk unit via a buffer in a subsystem control unit to provide an effective rapid access to the data by the hosts in an interleaved manner, such that the hosts do not see the delay of data transfer between the tape and the disk.

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Interleaved Data Transfers

In a storage type of subsystem, diverse memory devices are employed. For example, tape units are relatively slow-access devices; while disk units are relatively rapid-access devices. In transferring data between a host (CPU) and a memory unit of the subsystem, it is desirable that most transfers occur between the disk unit and the host unit. Accordingly, staging operations are employed between the tape unit and the disk unit via a buffer in a subsystem control unit to provide an effective rapid access to the data by the hosts in an interleaved manner, such that the hosts do not see the delay of data transfer between the tape and the disk.

With multiprogramming, data is usually requested before it is needed for execution. During the time interval, such data is transferred from a tape unit to a disk unit. When the data is needed by the host, the data in turn is transferred from a disk unit to a host. Additional time can be saved in the subsystem by further interleaving data transfers.

In transferring data between a disk unit and a host, a Start I/O (SIO) from the host starts the transfer. Upon completion of the data transfer, the subsystem control unit supplies a CHANNEL END signal to the host. This signifies that all data has been successfully transferred and the channel can be freed for other activity. However, in many instances, the disk unit has other activities to perform before a second data transfer can be effected.

Accordingly, the disk...