Browse Prior Art Database

Missing Address Mark Detector for Disk Files

IP.com Disclosure Number: IPCOM000076047D
Original Publication Date: 1972-Jan-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

King, RW: AUTHOR [+3]

Abstract

This detector is effective to indicate to the operating program for a CPU 8 that a sync area 9 or a part thereof cannot be read, particularly by noting that an incorrect sync byte 11 has been received.

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Missing Address Mark Detector for Disk Files

This detector is effective to indicate to the operating program for a CPU 8 that a sync area 9 or a part thereof cannot be read, particularly by noting that an incorrect sync byte 11 has been received.

Address marks 10 are especially generated groups of bits that can be recorded on disk drive 13 by disk drive attachment 15, positioned between disk drive 13 and CPU 8. Detection must be made of a missing address mark 10 for indicating to the program governing CPU 8 that a sync area 9 on disk drive 13 cannot be read. As may be noted from Fig. 1, the information on a disk may consist of an index marker, a home address (HA) and a plurality of records. Each record area consists of a count (CNT) area, a key area, and a data area, and there are gaps between each of these areas. Within each of these gaps, there is a sync byte 11 and two address mark bytes 10.

As shown in Fig. 1, no two consecutive sync areas 9 have the same sync byte 11 - the sync areas 9 differ in content depending in which gap they are contained. For example, the sync byte preceding the home address area is hexadecimal OD; the sync byte preceding the RO count area is hexadecimal OB; and the sync byte preceding each key area is hexadecimal OA. In the event that a sync area 9 or a part thereof is missed because it cannot be read by disk drive 13, the sync byte 11 that would have been read will be passed over, end the following sync byte which is in the next sync area 9 will be read into disk drive attachment 15. The detector utilizes the fact that disk drive attachment 15, under normal operating circumstances, is constructed to expect a particular sync byte 11 after a particular previous sync byte 11.

Referring to Fig. 2, the signal "sync restart" 19 and the signal "oriented" 23 are utilized on AND circuit 20 appended on latch 21 so as to provide the signal "missing address mark" 14. This signal indicates to the operating program that an address mark has been missed and that a sync area 9 cannot be read. It may be assumed that a read operation for reading record 1 (R1) is proceeding and t...