Apple ][ disk controller state machine

From: Chandra Bajpai <cbajpai_at_mediaone.net>
Date: Mon Sep 10 22:23:21 2001

I think the Lisa Twiggy shared the same encoding techniques and
variable spin rates that the 400K Mac drive/IWM combo had. I never looked
at
my Lisa 2 I/O board, but I wonder if it contains the same IWM chip.

Apple also upgraded the IWM in later Macs (~1987 or 89) to handle higher
disk densities.
The chip was renamed the Super IWM...I think the Mac IIci or IIfx was the
first of
Macs to get this new chip.

-Chandra

-----Original Message-----
From: owner-classiccmp_at_classiccmp.org
[mailto:owner-classiccmp_at_classiccmp.org]On Behalf Of Douglas Quebbeman
Sent: Thursday, September 06, 2001 8:25 AM
To: 'classiccmp_at_classiccmp.org'
Subject: RE: Apple ][ disk controller state machine


> Thanks, dq. I have seen that doc, but it speaks mainly of the
> 3.5 drive, which had several enhancements not available on the
> 5.25 drive. Was the Apple ][ controller sufficiently similar to
> the IIgs and progeny that this documentation is appropriate for
> it also? I've never heard the Apple ][ controller chip referred
> to as 'IWM' -- is that my ignorance, or was the chip renamed, or
> are they (maybe slightly) different beasts?

It's my understanding that the single-chip Integrated WOZ Machine
replaced and duplicated the function of the discrete-component-based
equivalent on the Apple II family...

FWIW, the Lisa 1 and the very first non-production Macs used a strange
5.25 inch floppy known as the Twiggy Drive... I can show you photos
of Macs that had been retrofitted for the 3.5 inch drives, but those
drives are visible through huge 5.25 inch gaping holes...

So while I can't say with certainty, I doubt the original circuit
has any capability not duplicated in the IWM chips.

Regards,
-dq
Received on Mon Sep 10 2001 - 22:23:21 BST