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Linked List Channel Control Words

IP.com Disclosure Number: IPCOM000087372D
Original Publication Date: 1977-Jan-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Covington, RP: AUTHOR [+3]

Abstract

Channel control words are stored in noncontiguous memory locations by adding a "linked address" field to each channel control word to designate the address of the next succeeding channel control word (CCW) to be processed by the channel for transferring input/output (I/O) data.

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Linked List Channel Control Words

Channel control words are stored in noncontiguous memory locations by adding a "linked address" field to each channel control word to designate the address of the next succeeding channel control word (CCW) to be processed by the channel for transferring input/output (I/O) data.

Microprocessor systems with teleprocessing applications are characterized by large numbers of relatively slow speed I/O devices. In such systems, efficient use of buffer resources requires that the buffers be pooled rather than dedicated on a one-to-one basis to the respective I/O devices.

A buffer pool contains all the available buffers in a system. As messages come in, they are placed in the first available buffer. Consequently, the buffer pool is a very dynamic structure; buffers are constantly being used and returned to the pool. Program management of the buffer pool is wasteful when using lists of CCWs where the CCWs are stored in contiguous storage locations. The size and order of the list is continuously changing. Consequently, excessive amounts of memory must be allocated around a given CCW for the unpredictable number of contiguous CCWs that are to be added in front of and behind the given CCW.

Efficient buffer pooling without excessive CCW memory allocation is achieved by utilizing CCWs that are processed sequentially by the channel without being stored sequentially in contiguous memory locations. A new field, termed a link address field, is adde...