| 摘要 |
981, 550. Digital data storage. INTERNATIONAL BUSINESS MACHINES CORPORATION. Nov. 21, 1963 [Dec. 24, 1962], No. 45922/63. Heading G4C. A system for correcting the reading of a block of data bytes from a record, e.g. a magnetic tape, which block has a parity check bit for each row and for each column, includes means for checking the parity of each row and each column, means to cause the record to be re-read and means to correct an erroneous bit if only one row and one column were in error on the previous reading. If two or more errors are simultaneously detected tape is re-read up to say 100 times to see if all but one of the errors can be removed by the cleanint effect of the tape read head. After 100 unsuccessful re-readings the tape drive is stopped by a counter or by a sub-routine of the computer for which the tape is being read. If only one row and one column are in error it is assumed that the error is due to a drop out and that a "one" bit is missing this "one" bit is inserted at an OR gate during the re-read cycle. Additional circuits selected by manually operated switches are arranged to prevent a correction if either further errors are detected during the re-reading or the error position shifts. Marginal dropouts are recovered as described in Specification 875,694. |
