Group Code Recording (GCR) is a data storage system for floppy disks, used by Apple II and Commodore computers in their 5¼ "drives for 8-bit computers (the most popular drives are the Disk II for the Apple II family and Commodore 1541, used by Commodore 64. It was also used by Apple Macintosh and Apple IIGS for their 3 "½" 400 "and" 800 "½" disks.
The purpose of GCR is to avoid too many consecutive zeroes (absence of transmission) because transitions synchronize reading time. GCR is more efficient than FM encoding, but less than MFM. Voices correlateemodify wikitesto
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