United States Patent
US Patent 4433388: Longitudinal parity
US 4433388 · granted 1984-02-21
| Patent Number | 4433388 |
|---|---|
| Title | Longitudinal parity |
| Filed | 1980-10-06 |
| Granted | 1984-02-21 |
| Inventor(s) | DuWayne D. Oosterbaan |
| Assignee | NCR Corp |
| CPC Classification | G06F11/08, G06F11/1004, G06F11/00 |
| Number of Claims | 3 |
Abstract
A memory system has a plurality of memory modules. A longitudinal parity word is stored in one memory module and correction words are stored in each of the other memory modules. When one of the data words in a memory module having a correction word is changed, the correction word is also changed from a prior value to a new value so that the longitudinal parity of the data in the modules is unaffected. The new value of the correction word is computed by EXCLUSIVE ORing the value of the data word before the change, the data word after the change, and the prior value of the correction word.
Claims Summary
1. In a data processing system having a plurality of memory modules, each memory module having a plurality of memory locations for storing data bits, said data processing system having a parity memory location for storing parity bits, the improvement comprising:a correction word memory location in each of said memory modules for storing correction word bits in each of said modules, the parity bits stored in said parity memory location being computed by logically combining said correction word bits with the data bits stored in said memory modules, so that a change in the data bits stored in one of said memory modules can be accompanied by a change in the correction word bits stored in that one memory module so as not to require a change in the parity bits stored in said parity memory location.