A 6K BPI disk storage system using MOD-11 interface

This paper describes an optimum equalized read channel for a 6300 BPI (2385.8 bits per cm) moving head disk file, the ISS/Univac 8434 disk drive. The system uses the standard MOD-11 interface and employs defect skipping which masks up to 3 media defects on any track. A new run-length limited code is employed. Its efficiency is 50% higher than the standard MFM. The data rate of the system is 1.26 MBytes/sec. The equalization is a method of spectral shaping to COS⁴Kf in the frequency domain. The theory behind this spctral shaping has its origin in communication theory. This equalization is discussed relative to several system parameters and functions and is shown to be optimum for each of these. Disk files have historically employed equalization in the write channel (prewrite compensation). The disadvantages of this method are discussed.