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Channel Command Word for Preformatting Fixed Physical Length Records on Direct Access Storage Devices

IP.com Disclosure Number: IPCOM000073682D
Original Publication Date: 1971-Jan-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Yates, LW: AUTHOR

Abstract

The described channel command of the write-special count, key, data type will preformat tracks for fixed-length physical records. Each record contains a count field, a key field and a data field. The count field of each record has the format CCHHRK(L)D(L)D(L), where: 1) CC is the two-byte cylinder number 2) HH is the two-byte head number 3) R is the one-byte record number 4) K(L) is the one-byte key length 5) D(L)D(L) is the two-byte data length. Since each track contains fixed-length physical records, then the CC, HH, K(L) and D(L)D(L) fields are identical for all records on the track, and the records differ only in the R field and the contents of the key and data fields.

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Channel Command Word for Preformatting Fixed Physical Length Records on Direct Access Storage Devices

The described channel command of the write-special count, key, data type will preformat tracks for fixed-length physical records. Each record contains a count field, a key field and a data field. The count field of each record has the format CCHHRK(L)D(L)D(L), where: 1) CC is the two-byte cylinder number

2) HH is the two-byte head number

3) R is the one-byte record number

4) K(L) is the one-byte key length

5) D(L)D(L) is the two-byte data length. Since each track contains fixed-length physical records, then the CC, HH, K(L) and D(L)D(L) fields are identical for all records on the track, and the records differ only in the R field and the contents of the key and data fields. The channel command word takes advantage of this by essentially incrementing the R field in the count field each time it executes a write count-key-data, thus allowing a channel program to preformat a data track with little storage space and with high speed. Initially, a search ID equal would be performed on record 0.

Thereafter a transfer in channel would be performed until the search ID equal was successful. After a successful comparison, a write count key and data command would be executed which would increment the R in CCHHRK(L)D(L)D(L) point was reached, indicating that the entire track had been formatted.

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