Re: Apple //+ floppy encoding method

[nparker@cie-2.uoregon.edu (Neil Parker)]

In article <5ane7h$pm2@ren.cei.net> kents@fs.cei.net (Kent Sutton) writes:
}[text reformatted to fit on 80-column display]
}I have read (and been told) that an Apple //+ (and other Apple // computers)
}cannot read/write an IBM compatible disk, and conversely, an IBM cannot
}read/write an Apple disk.
}Is this due to the nature of the hardware of the drive, or is it the drive
}controller?
}I have a computer that emulates an Apple //+ and an IBM PC equally well.
}It will read/write both Apple and IBM floppies in the same drive, and these
}disks are also useable in their respective machines.
}Is there something special about the drive?  It's a Shugart SA455.  Don't
}know the technical specs aside from the fact that it is half track steppable
}(maybe not the correct term).  In its native mode (CP/M 68K) this computer
}can format a 5.25" floppy in a dozen different formats, including an 80
}track, 800K format.
}I have no "grand design" here, just curious.

Hang on to that treasure!  Your friends who need Apple disks translated
into IBM format will thank you for it.

The incompatibility between Apple and IBM-compatible disks is at the
controller level.  Apple disks use GCR encoding, and IBM disks use MFM
encoding.  Neither controller can generate or recognize the timing required
to decode the other scheme.

Some controllers, of course, are capable of handling more than one encoding
scheme, and you obviously have such a controller in your machine.  There's
also one in recent Macintoshes, which can read IBM-formatted 3.5-inch
disks.

               - Neil Parker
-- 
Neil Parker, nparker@{cie-2,cie}.uoregon.edu, http://cie-2.uoregon.edu/~nparker
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