Group coded recording

In computer science, group coded recording or group code recording (GCR) refers to several distinct but related encoding methods for representing data on magnetic media. The first, used in 6250 bpi magnetic tape since 1973,[1][2] is an error-correcting code combined with a run-length limited (RLL) encoding scheme, belonging into the group of modulation codes.[3] The others are similar encoding methods used in mainframe hard disks or microcomputer floppy disks until the late 1980s. GCR is a modified form of a NRZI code, but necessarily with a higher transition density.[3]

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