It is probably an RLL scheme. MFM is for FAT/FAT12 disks. 5.25" & 3.5" 
floppy disks and very early hard drives. New hard drives uses an RLL scheme. 
If anything, for legacy sake, this would be an MFM/RLL style scheme versus a 
GCR/RLL scheme.

FAT was built around and on top of MFM coding so it is probably founded on 
this scheme for later FAT file systems for ease of software and hardware 
mechanics. If you take a look at Iomega SuperDisk project, it alludes to MFM 
and MFM/RLL encoding scehemes versus GCR because it doesn't read older GCR 
disks but MFM disks. So, this is probably the case.

GCR was Commodore, Apple II, and few IBM based systems: 
http://en.wikipedia.org/wiki/Group_Code_Recording



"Thomas Richter"  wrote in message 
news:gm8ril$e77$1{at}infosun2.rus.uni-stuttgart.de...
> Jack Tseng schrieb:
>> Iomega Zip disk itself is MFM or GCR ?
>
> It is whatever Iomega chose it to be, probably neither of the above. It
> is rather irrelevant, you cannot access the drive at this level anyhow,
> it either talks SCSI or ATA commands.
>
> So long,
> Thomas
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