Browse Prior Art Database

Internal Data Check Correction

IP.com Disclosure Number: IPCOM000035191D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Eggenberger, J: AUTHOR [+7]

Abstract

Disclosed is a method to correct some data checks within a DASD before transferring the data to the storage control.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 69% of the total text.

Page 1 of 2

Internal Data Check Correction

Disclosed is a method to correct some data checks within a DASD before transferring the data to the storage control.

To implement Internal Data Check Correction (IDCC), a DASD must employ a two-level Error Correction Code (ECC), data must be recorded as an integral number of equal-length ECC subblocks, and the DASD must include the following hardware: a buffer large enough to hold the data from one subblock, a series of exclusive ORs in which to perform data correction, and the necessary control logic. The IDCC buffer holds the data read from the data track while subblock check bytes generated during the read operation are compared to those previously written. Any discrepancy between the two sets of subblock check bytes will cause the data to be corrected in the exclusive ORs as it is moved from the IDCC buffer to the Data Transfer Buffer (DTB).

The key to IDCC is the arrangement of the check bytes at the end of a record. In the last subblock of a record, the Cyclic Redundancy Check (CRC) bytes of the block check bytes and any pad bytes necessary to make the record end on a subblock boundary precede the subblock check bytes. The remaining block check bytes are located at the beginning of the following gap. The subblock check bytes of the last subblock treat the CRC and pad bytes as part of the data. * Part of the Block Check Bytes ** Remainder of the Block Check Bytes

This arrangement of the check bytes and the added hardware allows...