Re: Monitoring Program

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

Ingo Soetebier <ingo@igd.fhg.de> wrote:

> David Empson wrote:
> > 
> > The original IIc firmware doesn't have a miniassembler.  It was added in
> > the revision which supports the UniDisk 3.5 drive (the second release).
> 
> It seems I have got the original firmware.
> 
> To ask another stupid question: Is the UniDisk 3.5 drive the disk drive
> that came with the Apple IIgs?

No.  That is the Apple 3.5 Drive.  The drives look a little different:

- The UniDisk 3.5 is plain white, like the IIc case, while the Apple 3.5
Drive is "platinum" (pale grey), like the IIgs or Mac SE and most later
Macs.

- The UniDisk 3.5 eject button is higher up on the case, and is
separated from the manual eject hole.

Both drives should be labelled underneath with the model name.

Internally, they use the same drive mechanism but a different interface
board.  The Apple 3.5 Drive is controlled directly by the host computer,
while the UniDisk 3.5 has an on-board CPU which controls the drive.  The
"SmartPort" protocol is used to communicate between the host computer
and the UniDisk 3.5's on-board CPU.

The 3.5" drive mechanism requires faster data transfer than Apple II
5.25" drives - the bit cells are 2 microseconds instead of 4.  This is
too fast for a 1 MHz Apple II to keep up with.  The IIgs is fast enough
to cope, but the IIc isn't.

The SmartPort protocol transfers data at the same rate as the 5.25"
drive (4 microseconds per bit), so it is possible for the IIc and other
1 MHz Apple II models to keep up with it.

> The Apple IIgs Drive works also on the Mac SE and has a eject button.
> (It's the only Apple 3.5" drive I've seen, which has an eject button.)

There is also the external SuperDrive, which looks exactly the same as
the Apple 3.5 Drive (apart from the label on its backside, and some
generational differences in the case and cable, such as a yellow LED
instead of a red one, and a larger moulding around the plug).

The Mac 800K internal and external drives also use the same drive
mechanism as both the Apple 3.5 Drive and UniDisk 3.5, but the external
drives have yet another variation on the interface circuitry, which
makes them incompatible with most controllers on the Apple II.  (The
exception is the Universal Disk Controller card.)

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