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Disk II & Disk III
Posted by: Mac128 on 2009-08-31 10:39:30
I recall reading a tutorial once about converting a Disk II to use directly on an Apple III, instead of buying the more expensive Disk III mechanism. But in recent Googling, I can find no reference to it, except a vintage supplier which mentions a modification to the Disk II's analogue board. Anybody know the exact differences? I always thought they were the exact same Shugart mechanism made more efficient by SOS.
Posted by: david__schmidt on 2009-08-31 14:12:31
There is a little bit of info on the Disk III and its use on a III+ here:

http://www.vintagemacworld.com/drives.html

but as for the Disk II, vintage photos show Apple employees with Apple III's with Disk II's hooked right to them (i.e. http://www.digibarn.com/collections/systems/appleIII/sandersinterview.html ). I too seem to recall there's an analog board difference, but the only functional difference is the "disk swapped" sensor to let the OS know the door had been opened.
Posted by: Dog Cow on 2009-08-31 14:40:31
I waited before I replied in case I was wrong, but I am pretty sure that the Disk ][ connects to a set of pins on the back of the ///.

See this pic: http://www.digibarn.com/collections/systems/appleIII/DSC06499.JPG

The blue port all the way on the left is where it would go.
Posted by: Mac128 on 2009-09-01 10:10:16
I am pretty sure that the Disk ][ connects to a set of pins on the back of the ///.The blue port all the way on the left is where it would go.
Um, nope. That is the Disk III connector. It is a 26 pin connector (25 pin on the III+). The Disk II has a 20 pin connector (or DB-19). So as I pointed out, it is NOT directly compatible with a Disk II. Apple did this on purpose to force Apple III buyers to buy the new drives rather than just replace the CPU and use with their existing peripherals. At a minimum, the pinouts have to be remapped. The first 20 pins of the Disk II & Disk III seem to be identical in function, suggesting that the 6 remaining Disk III pins are utilized solely for daisy-chaining up to three Disk IIIs. If this is the case, then only the connectors need be swapped as with the original Disk II to DB-19 connector for use on the IIc & IIGS.

vintage photos show Apple employees with Apple III's with Disk II's hooked right to them
I'm not sure that is proof of a Disk II being hooked right to them, without any modifications. This prototype is a perfect example of what was likely going on in-house while the /// was in development and likely even after the Disk III came out – the modified Disk II, or Disk III prototypes would not have been replaced with production models.
Posted by: david__schmidt on 2009-09-01 10:51:39
At a minimum, the pinouts have to be remapped. The first 20 pins of the Disk II & Disk III seem to be identical in function, suggesting that the 6 remaining Disk III pins are utilized solely for daisy-chaining up to three Disk IIIs.
Good point - it would need to be able to address all 4 drives. A little hint of an adapter is mentioned here:

http://news.altair.com/mailman/htdig/apple3-l/2004-March/000039.html

I'm not sure that is proof of a Disk II being hooked right to them, without any modifications. This prototype is a perfect example of what was likely going on in-house while the /// was in development...
Love the racing stripes! 🙂

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