Re: Apple Disk Drives

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

Douglas E. Morris <dmorris@doors.dnsalias.com> wrote:

> I am continuing to clean out the large pile of stuff that I got at the City
> Auction and have come to notice that I have 3 different types of 3.5" Disk
> Drives that are Apple drives.  Any help on what the difference is would be
> appreciated.
> 
> (1) Apple SuperDrive
> (2) Apple 3.5" Drive
> (3) Unidisk 3.5"
> 
> All seem to work with the Apple IIgs, but the Unidisk 3.5 causes me to get a
> message when booting system tools telling me it needs a driver, but it does
> identify the drive correctly.  Any help on what drive is best would be
> appreciated.

The Apple 3.5 Drive is the 'native' 3.5" drive for the IIgs, which was
sold with the machine if you bought a complete system.  It is the best
match if you are connecting the drive to the built-in drive port.

The UniDisk 3.5 is an intelligent drive: it has its own 65C02
microprocessor, and uses a packet-based protocol (SmartPort) to
communicate with the computer.  All data must pass through the internal
micro, so it is inherently slower than the Apple 3.5 Drive, and is not
compatible with some copy-protected software on the IIgs.  On the other
hand, it will work on an Apple IIc, and with Apple's original "Apple 3.5
Floppy Disk Drive Interface Card" on the IIe.

Both the Apple 3.5 Drive and UniDisk 3.5 will work with 400 KB and 800
KB 3.5" disks: single or double sided respectively, double density in
both cases, using Apple's GCR data coding scheme and variable rotation
speeds, physically compatible with 400K and 800K disks on the Mac (you
just need software to support the Mac's file system, which is MFS for
400K disks, HFS for 800K disks).

The Apple 3.5 Drive and UniDisk 3.5 actually have the same mechanism -
the only difference is the interface board inside the drive case.

The SuperDrive is an upgraded version of the Apple 3.5 Drive.  It adds
support for MFM disk encoding (720 KB for double density) and high
density disks (1.44 MB) at fixed rotation speeds (compatible with the
PC).  To use these extra features with the IIgs, you have to connect the
drive to the later (and much rarer) controller card from Apple.  (Its
official name is "Apple II 3.5 Disk Controller Card", and is
colloquially called the "SuperDrive Card".)

If you connect a SuperDrive to the built-in disk port on the IIgs, it
will appear to be an Apple 3.5 Drive as far as the computer is
concerned, and will work fine (without the extra features).