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New Channel Command Words for Data Base Operations

IP.com Disclosure Number: IPCOM000085802D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 4 page(s) / 45K

Publishing Venue

IBM

Related People

Witt, DE: AUTHOR

Abstract

Three new channel command words (CCW's) are described for extending channel architecture, to enable data base type input/output (I/O) functions to be performed more easily and with improved performance and concurrency.

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New Channel Command Words for Data Base Operations

Three new channel command words (CCW's) are described for extending channel architecture, to enable data base type input/output (I/O) functions to be performed more easily and with improved performance and concurrency.

With the growing demand for online data base/data communication (DB/DC) functions, new demands have been made on operating system performance. Highly used functions, such as searching of data bases, queues or other stored files requires the logic capabilities of the central processor unit (CPU). This can cause degradation due to the channel restarting required to mix channel and CPU capabilities.

The essence of the present proposal is the addition of three new channel command words to the system architecture, to allow the execution of limited logic during the channel program execution.

The first new channel command word (CCW) enables the specification of search arguments to be used by the channel to examine any part of the data transferred to main storage, and provides a capability to change the execution path of a CCW chain resulting from this examination.

The second new CCW aids the continuation of search I/O by providing a means of saving the current record address, thus giving a restart point for ensuing operations.

The third new CCW implements a means of supplying the channel the full set of data extents for which an I/O operation is valid. This minimizes the software I/O supervisor's intervention in the complete CCW chain execution.

These new CCW's enable an access method to build a channel program which will be able to select records to be returned, fill multiple buffers, and record restart points for following operations.

The entire I/O operation is under channel control and requires no intermediate intervention by the CPU.

The facility to allow the examination of data being read is a new CCW called TEST DATA RECORD. Its format is shown in Fig. 1.

The CCW address field contains the address of a DATA PARAMETER LIST (DPL). This list contains the addresses of data which will be logically compared much like a CLC compare logical instruction. The format of this list is one or more word pairs. The high-order byte of the first word contains the data length, while the low-order three bytes of both words contain data addresses. The high- order byte of the second word of the first word pair contains two bits indicating the desired result of the compare operations: high, low or equal.

The flags field of the CCW are unaffected. The data length field of the CCW contains the length of the DPL.

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The data described by the first word of a word pair in the DPL is compared to the data described by the second word. Any mismatch terminates the operation with the appropriate result, otherwise, once the length of the data is exhausted, the next pair of words are used in a similar manner. The DPL length is determined by the data length field in the CCW. Once it has bee...