MAGNETIC STRORAGE SYSTEM USING ALTERNATE CODES TO REDUCE WRITE CURRENT BIAS

1382515 Digital data recording HONEYWELL INFORMATION SYSTEMS Inc 28 Sept 1972 [3 Jan 1972] 44926/72 Heading B4C A digital data recording apparatus and method is disclosed. Digital data is recorded on a magnetic disc in groups of three bits, each group being represented by a pattern of four possible flux reversal positions (Fig. 2). In each pattern there are at least two reversals and, in a pattern, there are not more than two positions without a flux reversal. Three groups of bits, 001, 011, 110 can each have two possible patterns. The data is recorded as alternate control groups (bits 001) and data groups and alternate control groups set a control circuit. When the control circuit is set, the groups, 001, 011, 110 have a different pattern to when the control circuit is not set. The purpose of this is to prevent excessive D.C. bias when deposited film type transducers are used. Encoding and decoding logic, possibly using ROM'S connected to a computer, is described.