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Least Time Accessing of Disk Files

IP.com Disclosure Number: IPCOM000092009D
Original Publication Date: 1968-Aug-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Comeau, LW: AUTHOR

Abstract

An associative memory is employed to minimize the time required for accessing data stored in disk files in a multiprogrammed data processing system.

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Least Time Accessing of Disk Files

An associative memory is employed to minimize the time required for accessing data stored in disk files in a multiprogrammed data processing system.

In a conventional multiprogrammed system, the channel command words CCW's, fetched by the various programs, are stacked or queued in memory and are accessed in the same order as they are stacked, i.e., first-in, first-out. Not infrequently the CCW being accessed contains a data address in disk storage which, at that instant, is separated by a large radial distance from the respective read-write head. Thus the arm carrying this head must take a correspondingly large amount of time to reposition itself radially at the addressed track. This tends to increase the average access time. In this arrangement, the stacked CCW's are accessed in such a way that the CCW chosen for execution is the one whose data address involves the least radial movement of a disk file arm, thus reducing the average access time. Suitable precautions are taken, however, to insure that none of the stacked CCW's is ignored for an unduly long time.

Control unit 1, associated with a group of disk modules such as 2 and 3, is arranged to include queuing device 4 containing queue logic circuitry for operating a small associative memory 5 and local store 6. The various fields of memory 5 and store 6, ignoring their actual geometric orientations, are laid out as in the right-hand drawings.

As each positional CCW is fetched by the control unit and queued in local memory, the disk module number of the data address contained in that CCW is entered into an appropriate field of memory 5 at the next available byte address in it. At the corresponding byte address of store 6, the main memory addres...