8–9 Block Code: A DC-Free Channel Code for Digital Magnetic Recording

This article describes the 8–9 block code, a dc-free channel code for use in digital magnetic recording. The coding strategy is discussed, as well as results of investigation of the properties of the code by computer simulation and hardware experiment. This code can be applied to a digital VTR without major modification to the recording and playback circuits which were previously used for the 8–10 block code. Although further study is required for selecting the best channel code for the digital VTR, the 8–9 block code may be considered a reasonable compromise between the 8–10 block code and the 8-bit code without overhead.