GB1529583A - Data processing system - Google Patents

Abstract

1529583 Data processing system XEROX CORP 6 Oct 1975 [29 Oct 1974] 40810/75 Heading G4A The description is similar to that of Specification 1,529,581 except that it contains additional material relating to the disc store controller. The claims relate to a microprogram controlled disc system including a disc controller operated under microprogram control, each command being verified as valid before being executed. The disc controller operates under microprogram control to read data from and write data on to a disc storage system including one or more double-sided discs. Three independent data blocks are recorded in each recording position along a disc track, the first two words including the address, the next eight words being a label, and the remaining 256 words being data. The data may be checked by comparison with that in the main data store except that certain words may be omitted from the checking in order to permit read and checking operations to be combined. A four word block in the main memory includes a pointer to a chain of disc commands, the controller idling when the pointer is empty, i.e. O. The disc commands consist of ten words which include a pointer to the next command, O indicating that this is the last command, status data, the command, disc address data, pointers indicating the location, or required location, in the main memory of the data, and words controlling the initiation of interrupts when the command has been completed. Each command accessed is verified as valid by comparing it with a verification word stored in a constant memory defore being executed. The discs are divided into sectors, e.g. 12 per track and sector and word signals are used to interrupt the microprogram (task switching, see Specification 1,529,581) in order to keep track of the addressing of the disc. Error signals also cause interrupts. The Specification gives some detail of the various circuits used in the disc controller.