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From: toddpw@nntp-server.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple2
Subject: Re: 1.44 vs 1.60 MB 3.5 formatting
Message-ID: <1990Dec9.130157.10685@nntp-server.caltech.edu>
Date: 9 Dec 90 13:01:57 GMT
References: <9012081825.AA06808@hilbert.grin.edu>
Organization: California Institute of Technology, Pasadena
Lines: 27

throop@hilbert.UUCP (Henry Throop) writes:

>Maybe this has been discussed before, but I don't remember seeing it.  Does
>anyone know what the format of a 1.44 MB floppy is based on?  Is it the same
>as a 720K (IBM) 3.5, but just with twice the number of tracks, and thus 
>a constant angular velocity?  Or is is some variant on the 800K formatting?
>Are Mac and IBM 1.44 disks readable (sector-wise) by the same drives?

What I do know:

IBM drives are CAV, and the Apple drives aren't.

For the actual bit encoding on the disk, IBM drives use MFM as opposed to
the GCR used by Apple drives before the FDHD. These encodings are how the
bit stream actually appears as pulses on the disk, and are generally
implemented in hardware. MFM is a simple technique, but GCR stores about 20%
more data on the same disk. The difference between the two is basically a
change in the digital state machine that sits between the disk interface
and the actual drive head.

Apple's push towards IBM formats is because of their business thrust. I
gotta admit it would be nice to read IBM formats, but to do it AE would
have to make what would amount to a beefed up Unidisk. AE is opting
for performance and storage rather than IBM compatibility.

Todd Whitesel
toddpw @ tybalt.caltech.edu