An experimental, multilevel, high density disk recording system

Communication technology has been applied to a magnetic disk recording channel to achieve up to a fourfold increase in linear bit density as compared to conventional binary recording. Among the techniques incorporated were digital data transmission by Class IV Partial-Response signaling (Interleaved NRZI), recording channel pre-emphasis, equalization and filtering, and periodic amplitude sampling of the data signal. The magnetic recording channel was linearized using very high frequency a.c. bias, which also served simultaneously to erase old data. This enabled multilevel recording and the addition of a pilot tone for timing recovery. System block diagrams are presented together with a discussion of the optimization procedure and attained system performance.