GB1169506A - Improvements in or relating to Magnetic Memory Systems. - Google Patents

Abstract

1,169,506. Electric digital data-storage. NATIONAL CASH REGISTER CO. 20 May, 1968 [23 June, 1967], No. 23879/68. Heading G4C. In a magnetic memory system comprising a recirculating magnetic surface having a plurality of annular storage tracks, a transducer is moved transversely of the tracks to the required track(s) under control of track address signals derived from tracks during the transverse movement. In a magnetic disc file, a head assembly for a removable stack of 3 discs holds 12 heads for each of 6 disc surfaces and can be positioned at any one of 16 radial positions to co-operate with a corresponding one of 16 sets of 72 tracks. Each 72 tracks comprise 64 data tracks, a label track and 7 spare tracks. Each disc surface is divided into 8 sectors. A computer supplies an address having zone, cylinder and sector portions, the head assembly being moved radially in the appropriate direction as the discs rotate until positioned on the required set of tracks, specified by the zone and cylinder portions which are compared with zone and cylinder indications read from each (or every fourth) label track crossed until equality is obtained, notice being taken of the comparison results only on a portion of the width of a label track near its leading edge (encountered radially) under control of a cam driven by the head assembly motor, thus ignoring false signals at the junctions between tracks and enabling the head assembly to stop centrally on the required set of 72 tracks. The required sector is now obtained by comparison with sector addresses read from the label track of the set of 72 tracks reached, as the discs rotate. Each sector of each label track holds its zone, cylinder and sector address, and repetitive bit patterns for clocking, synchronization and data preamble and postamble. Some of these are used in recording data, sync. bits and data preamble (used for setting the gain of the read amplifier during read-out) and postamble in sectors of data tracks. If a plurality of consecutive sectors are required, the sector comparison is done only for the first. The number of sectors is preset by the computer into a counter which is then counted down. A plurality of disc units can be controlled via a common controller from the computer, each unit having two files, each as above, circuitry being shared between the two files to some extent. The controller incorporates serial-to-parallel conversion and the reverse for data transfer from disc to computer and the reverse respectively. Drum storage could be used in place of disc. Self-clocked recorded signals may be used.