Re: PCT, low-density disks, and Apple 3.5 drives

[dempson@actrix.gen.nz (David Empson)]

Bruce Maples <themaples@worldnet.att.net> wrote:

> Just a question --
> 
> If PC disks are MFM, and Apple disks are GCR, then how does the PC
> Transporter use an Apple 3.5 drive to read and write low-density
> (720k) disks?

It has an early version of the "SWIM" disk controller chip, which
supports GCR and MFM disk formats.

I suspect the PC Transporter also has some special hardware to cope with
the variable rotation speed of the Apple 3.5 (without any special
support, it would not be possible to accurately read a 720K disk, let
alone write one).

> And, if the Apple 3.5 can be used to read PC 720k disks

[Only with special hardware support]

> would it be possible to write a utility on the PC to write 800k
> ProDOS disks?

No.

> Why or why not?

Because the PC disk controller hardware can only handle the MFM
recording format, and the PC 3.5" drive doesn't vary its rotation speed.
To support the Apple II GCR format you need a special controller that is
more flexible than a standard MFM disk controller.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand