Write equalization for generalized (d,k) codes

The write-equalization method for the (0,3) code used in the IBM 3480 magnetic tape subsystem adds pulses for each zero in such a way as to preserve a two-level write-current. A similar but generalized method of write equalization that is applicable to all (d,k) codes which (N-d) pulses are added between the NRZI transitions (N is the number of zeros between transitions and d is from the (d,k) constraints). It is shown that the write-equalization algorithm produces a transfer on the write side that does not change with the data pattern even though pulses are added for some but not for all zeros. The transfer functions discussed give varying amounts of high-frequency boosts on the write sides. As a result, the signal-to-noise ratio at the detector can be increased when a write equalizer is used, because less high-frequency boost is required on the read side. Examples are given for a (1,7) code. Extensions to (2,7) code and to the more general case are also presented