Electronic digital computing machines

979, 633. Digital computers. NATIONAL RESEARCH DEVELOPMENT CORPORATION. April 19, 1961 [April 20, 1960], No. 13855/60. Drawings to Specification. Headings G4A and G4C. In a modification of the data storage arrangements described in Specifications 976,499 and 979,632 in which, if a required word is not present in the main store, an automatic transfer operation is initiated to transfer the block containing the required word from the secondary store to the main store and to transfer a block from the main store to the secondary store, the block selected for transfer from the main store to the secondary store is chosen on the basis of the period of time it has been located in the main store without use having been made thereof. For this purpose, two counters are provided, each stepped on each time the machine performs an instruction but one of which is reset each time a predetermined count is reached to interrupt the normal programme and adjust records of the time each block in the main store has remained unused. A record is also kept of the time each block now in the main store had previously been in the secondary store. When a transfer operation, as described in Specification 979, 632 is signalled, the records for the various blocks in the store are compared to determine which block is to be transferred from the main to the secondary store.