3.5" Unidisk Info -miniFAQ's

Mackduncan writes... 
>Will the ][c's ONLY accept a Unidisk? 

In terms of a 3.5 floppy drive, yes. It can also work with smartport 
hardrives, like the Pro-App and Chinook CT-series. This excludes the 
original ROM verison of the IIc (identified as '255' if you type "PRINT 
PEEK (64447)" from the Applesoft prompt) which can only add an external 
5.25 drive. 

>I use the ][c+ and that one is very similar to the ][GS. 

Relatively speaking, the IIc Plus is an altogether different machine 
from IIc. It can use all the same devices as the IIc (UniDisk 3.5, 
Smartport HD, Apple 5.25 and compatibles) as well as the grey Apple 3.5 
that works on the IIgs (and Mac's, circa 1986-92). The reason it *can* 
use the Apple 3.5 drive is due to the fact there is added circuitry on 
the board and a faster processor to handle it. 

>What will the Unidisk do that the Platinum 3.5 not do? 

It'll work on an Apple IIc. The UniDisk 3.5 is an "intelligent" drive, 
in that addition to the same Sony 800K floppy mechanism and daisy-chain 
card inside, it has an analog board with 65C02, ROM, RAM and an IWM. You 
see, the IIc is too slow to deal with data being sent from an Apple 3.5 
drive (it's a "dumb" drive btw, since all the brains to handle it are 
inside the IIgs or Mac) so the UniDisk 3.5 drive itself decodes it 
before sending it along to the IIc. 

The Unidisk 3.5" has a "slow down" interface to accomodate 
the floppy speed to the slow standard IIc.
The disadvantage is the UniDisk 3.5 operates at only about half the 
speed of an Apple 3.5 whether connected to a IIe (with "Liron" 
controller), IIc or IIgs, but as mentioned, it is the only option for a 
3.5 drive on a IIc.