Re: 3.5" drives on the IIc (was Re: n)

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

In article <4pf189$3j8@gateway.ecn.com>,
OCTAVIO Z <octavio@gateway.ecn.com> wrote:
> Yes, hello, I want to know if I can use my Macintosh's 3.5 800k disk 
> drive on my Apple IIc...Instead of the Unidisk 3.5?

Deja vu!  Didn't I just answer this question about a week ago?  Perhaps
that was in E-mail.

No, you cannot use a Mac 800K drive on a IIc.

> What is the diffrence between the UniDisk 3.5, and teh regular 3.5
> 800k?

The UniDisk 3.5 is the same as the Apple 3.5 Drive, with one
exception: they have different circuit boards which handle the
interface to the computer.

The UniDisk's interface board has its own microprocessor, RAM and ROM.
The microprocessor on this board is responsible for controlling the
drive hardware, and for communicating data with the computer.

By comparison, the Apple 3.5 Drive has a simple circuit board which
arranges things so that the computer is directly responsible for
controlling the drive hardware.

The UniDisk requires much less work on the part of the computer,
because all the hard stuff is handled by the microprocessor inside the
drive.  The UniDisk also has a lower data transfer rate to and from
the computer (4 microseconds per bit vs 2 microseconds per bit for an
Apple 3.5 Drive).

A 1 MHz Apple II cannot cope with data transferred faster than 4
microseconds per bit, so you cannot use an Apple 3.5 Drive (or
equivalent) on a IIe or IIc, unless you have a controller which runs
at a higher clock speed (e.g. the SuperDrive card for the IIe/IIgs).

The IIc has no way to use an interface card, so it is not possible to
use an Apple 3.5 Drive.

In the IIgs, the Apple 3.5 Drive is supported because the disk
accesses are performed with the processor running in "fast" mode (2.8 MHz).

The IIc+ has a built-in Apple 3.5 Drive, and supports an external one.
It is able to do this because it has a special controller chip that
takes most of the load off the processor.  The processor also runs at
4 MHz (the equivalent of a ZIP Chip is built into the communicator).


In addition to the consideration of UniDisk 3.5 vs Apple 3.5 Drive,
there is another problem: the Macintosh 800K drive is not fully
compatible with the Apple 3.5 Drive.  It doesn't provide some of the
signals expected by the standard Apple II 3.5" drive controllers
(IIc+, IIgs, SuperDrive card).

> Also, can I upgrade my IIc by putting more memory in?

Yes.  If you have the original IIc motherboard, there is a 1 MB RAM
card made by Applied Engineering called the "Z-RAM", which plugs into
the CPU and MMU sockets under the keyboard.

If you have the later "memory expandable" IIc, there is a special
memory expansion slot, which will accept an Apple IIc 1 MB memory
expansion card made by Apple.

You can check if you have the latest motherboard by getting into BASIC
and typing PRINT PEEK(64447).  If it says 3 or 4, then it is almost
certain that you have the new motherboard with the memory expansion slot.

> Give me an idea how or what I need to do to upgrade to a IIc+!

The only way to "upgrade" to a IIc+ is to replace the whole computer.
The IIc+ has a different case, different motherboard, built-in 3.5"
drive, probably a different keyboard, and a built-in 110V power supply.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand