Re: Apple 3.5" drive questions

[Eric Smith <eric-no-spam-for-me@brouhaha.com>]

"Charlie" <charlied@NOSPAMbboard.com> writes:
> This made me
> wonder for the millionth time if software could solve the problem of
> reading and writing MS-DOS with an 800k Apple 3.5" floppy drive
> connected to an Apple II.

> Yes, I know, this is supposed to be impossible.  The hardware is
> supposed to be incompatible with writing MS-DOS.
> 
> What I don't know is why.

Because the Disk II controller (and all the other Apple II floppy
controllers except the SuperDrive/FDHD controller) can only support GCR.
They can't do MFM.  This has nothing to do with the drive.

Actually the Disk II controller can sort of support FM (single density)
since the data patterns are a subset of those used in GCR.  However, it
can't really support the industry-standard IBM 3740 format.

When Woz designed the Disk II controller, compatability with disks
for other systems was not a major consideration.  He was mostly trying
to make it simple and inexpensive, and succeeded admirably.  If you
wanted compatability, there were third-party controller cards which
could do that.