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Transparent Repositioning of Access Mechanism from Defective to Alternate Track

IP.com Disclosure Number: IPCOM000077856D
Original Publication Date: 1972-Oct-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Hancock, RJ: AUTHOR [+2]

Abstract

The circuitry controlling a Direct Access Storage Device (DASD), or the like, can reposition the DASD access mechanism from a defective track to the assigned alternate track, and thereafter reposition the access mechanism to the next track after the defective track, without requiring CPU interrupt. This technique can be used if data transfer has not been initiated on an overflow operation.

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Transparent Repositioning of Access Mechanism from Defective to Alternate Track

The circuitry controlling a Direct Access Storage Device (DASD), or the like, can reposition the DASD access mechanism from a defective track to the assigned alternate track, and thereafter reposition the access mechanism to the next track after the defective track, without requiring CPU interrupt. This technique can be used if data transfer has not been initiated on an overflow operation.

The Track Descriptor Record (RO) of the defective track contains the physical address of the assigned alternate track, while RO of the alternate track contains the physical address of the corresponding defective track. RO of each track contains a defective track indicator and an alternate track indicator.

When the command is received from the channel, the control circuitry checks the defective indicator for the track. If the indicator is present, the control circuitry informs the channel to reissue the command after ending status is presented. The physical address of the assigned alternate track is obtained from the above- mentioned count field, and the control circuitry positions the access mechanism to that physical address. When the transducer is oriented on the track, the alternate track has been achieved. Ending status is sent to the channel and the operation continues with the command being reissued.

The alternate track indicator of each track is checked after checking the defective track indi...