Gator@cup.portal.com (Walter Thomas Reed) (03/29/89)
>> >What about GCR? >> It writes the same number of bauds as MFM so no net gain. >The one Apple uses on the ][ does, maybe, but there are denser GCR codes >available and they're supposed to be more resistant to noise than MFM and >RLL. Well, according to Amiga Disk Drives Inside and Out (by Abacus) the amiga cannot handle several one bits following each other, so the recording density is changed to half speed (4ms/bit instead if 2ms.) Does this mean that GCR is less effecient than MFM and you actually get less storage? The book was unclear about that. Walt
w-colinp@microsoft.UUCP (Colin Plumb) (04/03/89)
Gator@cup.portal.com (Walter Thomas Reed) wrote: > Well, according to Amiga Disk Drives Inside and Out (by Abacus) > the amiga cannot handle several one bits following each other, so the > recording density is changed to half speed (4ms/bit instead if 2ms.) > > Does this mean that GCR is less effecient than MFM and you actually get less > storage? The book was unclear about that. As my original article mentioned, it's a limitation of the oxide on the floppy. Given that 4us between one bits on the innermost track of a 90 mm floppy spinning at 300rpm is the minimum, we can translate this into distance. Assume the innermost track has a diameter of 50mm, that gives you 50*Pi mm of track to fit the 0.2s/4us = 50,000 1 bits on to, that gives you 50*Pi/50,000 mm = Pi um of track per flux change. Since the 50mm is only a guess, round it to 3um. Tha Amiga hardware will let you write consecutive 1 bits at 2us times, the floppy just won't remember it. Anyway, yes, the traditional 5/4 GCR (4 bits encoded as 5) format is less efficient than MFM. It can fit 4 bits into 20us, while MFM can fit 5. -- -Colin (uunet!microsoft!w-colinp) "Don't listen to me. I never do." - The Doctor