Talk:Group coded recording

message: Perhaps it's worth noting that while the 1541 used constant angular velocity, it did vary its data rate to keep the data density near the maximum across all tracks.  Compare this with the PC, which really did space bits further out on outside tracks, and CD-ROM drives, which started out Mac-style and changed to 1541-style in the mid/late 90s.
--2004-11-27T20:17:31‎ 84.43.5.61
:GCR Didn't start with CBM. GCR was being developed before Commodore deployed it on their drives.  The Durango Systems F-85 (introduced in late 1976) boasted 500K per 100 tpi floppy using 4/5 group code; eventually expanded to a double-sided option boasting almost 1MB per diskette. A few years before this, Sperry ISS was working on large hard drives for the mainframe business using group coding.
:--CG (2004-12-10T22:09:54‎ 65.102.127.71)
::GCR being thought of as originally a floppy format says something about which generation many Wiki editors (including me) belong to.  It was around as early as 1973 (with the IBM 3420/3803 models 4,6, and 8), as a tape format for 6250 BPI drives.  Wozniak re-invented a much simpler form for the Apple II with 5-and-3 and later 6-and-2 codes.  I don't know where CBM got their code, which had 5 disk bits for 4 data bits; perhaps they didn't have an 8-bit data latch as a constraint.  
::Jackpot-- I found one of IBM's papers on the subject: http://www.research.ibm.com/journal/rd/186/ibmrd1806Q.pdf.  IBMs GCR is way more complex than the CBM or Apple versions, as it not only satisfies physical constraints but provides error correction as well.
::--Nybbler 23:20, 25 February 2006 (UTC)
replies: text:  Chuck, just a small sidenote, based on magazine announcements and George Comstock's interview, the Durango F-85 was introduced in September 1978, not 1976. Based on the same sources, Durango was started in 1977. It is still possible, however, that Comstock left Diablo in 1976, as stated on your web-site. As several GCR-floppy related products were introduced around 1977 to 1978, the dates may become important if we want to establish something like a GCR timeline or chronology. --Matthiaspaul (talk) 15:39, 21 June 2017 (UTC)
thread_title: 1541's pioneering scheme of CAV + varying data rate

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message: For historical completeness it would be great if we could add the actual GCR codes used by the Durango, Brother and Sharp floppy controllers. Unfortunately, I could not find any documents listing these codes so far. Are the Durango and Micropolis GCR codes the same?
Regarding the Sirius/Victor codes, I have found references indicating that they are byte-wise identical to the Commodore codes and others indicating that they are "almost" the same but differ in nuances. To settle this once and for all, I'm still looking for a Sirius- (not Commodore-)related RS listing the codes explicitly.
Have there been any other (possibly obscure) floppy formats using some form of GCR?
More info on GCR coded hard disk formats would be appreciated as well.
--Matthiaspaul (talk) 13:56, 19 April 2017 (UTC)
thread_title:  Durango, Brother and Sharp GCR codes missing 

message: Several years ago, the following comment was added to the Talk:Magnetic_tape_data_storage#Potter_Instruments page. I'm copying it to here as it may give some pointers to further research the early history of GCR encoding: --Matthiaspaul (talk) 15:26, 21 June 2017 (UTC)
replies: text: It is rather odd and sad that Potter Instruments, with its many, many contributions to magnetic tape (and disk) recording technology is all but forgotten. The company folded in the seventies. They held hundreds of patents including 6250 GCR which was done for Burroughs. They were another of the "plug compatable" tape, disk and printer manufacturers  during the sixties, early seventies. IBM used (under license) many of those patents. Woodym1 (talk) 00:29, 6 October 2008 (UTC)
thread_title:  GCR and Potter Instruments 

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thread_title:  External links modified 

message: A discussion is taking place to address the redirect :"6 and 2" encoding. The discussion will occur at Wikipedia:Redirects for discussion/Log/2020 September 14#"6 and 2" encoding until a consensus is reached, and readers of this page are welcome to contribute to the discussion.  Steel1943 (talk) 17:48, 14 September 2020 (UTC)
thread_title:  ""6 and 2" encoding" listed at [[Wikipedia:Redirects for discussion|Redirects for discussion]]