Method for providing a substitute memory in a data processing system

Claim 1

In a data processing system having a central processor and a plurality of memory modules, each having data initially stored therein, each callable by a unique address, and each having a comparator to cause access to the memory module upon occurrence of a match between an address called by the central processor and the unique address, a method for substituting a designated one of said plurality of memory modules for any other of said plurality should the latter become faulty while said system is in operation comprising the steps of: (a) retrieving from said central processor the unique address of said another memory module upon detection of a faulty in the latter and storing it into a register; (b) transmitting a permanent space-in-use signal to each of said memory modules; (c) transmitting a match signal to all memory modules upon occurrence of a match between a called memory module address and the address in said register; and (d) by means of logic circuits in each of said memory modules: (i) preventing access to said another memory module when called in the presence of a spare-in-use signal; (ii) preventing access to said designated memory module when called and the spare-in-use signal is present; and (iii) permitting access to said designated memory module only in the presence of both the spare-in-use signal and said match signal.