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Reservation of Logical Storages by I/O Channels

IP.com Disclosure Number: IPCOM000076331D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Capowski, RS: AUTHOR [+3]

Abstract

High-speed rotational devices are subject to overrun when the channel to which they are attached is delayed in completing its storage request. This delay is caused by interference from the central processing unit and from input/output devices operating through other channels contending for the same logical storage. The exposure to overrun is alleviated by reserving main storage far enough in advance of the actual request for storage by the channel to insure minimum interference at the time of the request.

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Reservation of Logical Storages by I/O Channels

High-speed rotational devices are subject to overrun when the channel to which they are attached is delayed in completing its storage request. This delay is caused by interference from the central processing unit and from input/output devices operating through other channels contending for the same logical storage. The exposure to overrun is alleviated by reserving main storage far enough in advance of the actual request for storage by the channel to insure minimum interference at the time of the request.

The main storage is interleaved among four logical storages, such that requests for contiguous addresses in main storage can be honored at a rate equal to the machine cycles until all logical storages become busy.

A storage priority logic is provided to resolve priority among storage requests for each logical storage independent of all other logical storages. Thus, a separate queue of requests is maintained for each logical storage.

A high-speed priority line from the channel is provided which precedes the channel request by one storage cycle, to thus initiate the reservation logic. The first priority request reserves all logical storages, because there is no way of knowing which logical storage will be requested by the channel. After the first request by the channel, the next logical storage is known and thus, when the reservation line is raised for the next request, the next sequential logical storage only is res...