1A Processor: Memory Systems

1.1 Memory hierarchy The 1A Processor memories are call stores (CSs), program stores (PSs), file stores (FSs), and tape. The program and call stores are very similar in hardware. The main difference is a two-word or 52-bit output from the PS and a one-word or 26-bit output from the CS. The PSs contain programs that are normally resident and paging areas that are used for only occasional programs. The CSs are for transient data and for translation data. Each CS containing transient data is duplicated 181 in core while translation CSs are simplexed with the data duplicated in disk. In case of a PS failure, a roving PS spare is substituted and pumped up with program from the file store. Failure of one of a fully duplicated CS pair does not involve a pump up from the FS. Failure of a simplex CS calls for replacement by one of a duplicated CS pair and a pump up from the F S . The file store is used as a source of data and programs and, in addition, it is used to accumulate data. The file store is essentially nonvolatile; i.e., the contents can be trusted when first powered up. A new unit of memory must be written when first installed. The source can be either the duplicate unit or tape. The tape units are part of the auxiliary data system ( A D S ) . The tape units are used to accumulate data and to supply program and translation data to the store.