| 摘要 |
<p>1440285 Error correction INTERNATIONAL BUSINESS MACHINES CORP 24 April 1974 [4 June 1973] 18002/74 Heading G4A Data is stored on a plurality of independently accessible storage units, e.g. magnetic tape cartridges, and check bits, each of which is a function of a corresponding bit from each data storage unit, are stored on a check unit which may be used, in the event of a catastrophic loss of data on one of the data storage units and detected by an error checking facility associated with that unit, to restore the data on that unit. Extension of the system to include more than one check unit, each of which stores the check bits for one position of a Hamming code, is also mentioned. In normal operation, one of the data storage units is selected and data thereon is updated by read before write heads 15, 21. The difference e jk between each old bit and the corresponding new bit is EXORed with the corresponding old parity bit p k from the check unit to update the parity bits. The parity bits are initially recorded by successively (or simultaneously) reading the data storage units to record the modulo 2 sums of the corresponding bits, and data restoration is similar reading from the good data storage units and the check unit.</p> |
