Jump to content

Group coded recording

From Wikipedia, the free encyclopedia
This is an old revision of this page, as edited by 66.169.103.126 (talk) at 23:02, 24 September 2005 (avoid redirect). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Group Code Recording (GCR) is a floppy disk data encoding format used by the Apple II and Commodore Business Machines in the 5¼" disk drives for their 8-bit computers (the best-known drives being the Disk II for the Apple II family and the Commodore 1541, used with the Commodore 64 computer). It was also used on the Apple Macintosh.

The purpose of GCR is to avoid too many consecutive zeroes (i.e. absence of transitions), because the ones (transitions) synchronize the read clock. GCR permits consecutive ones.

GCR is more efficient than FM coding, but less efficient than MFM. Because MFM does not permit consecutive transitions, it runs at twice the clock rate of GCR.

See also

Retrieved from "https://en.wikipedia.org/w/index.php?title=Group_coded_recording&oldid=23947300"