Disk II & Disk III

[Mac128]

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.

 

[david__schmidt]

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.

 

[Dog Cow]

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.

 

[Mac128]

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.

 

[david__schmidt]

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!