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IIGS "Unidisk" vs a standard 3.5 drive

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#1 eightbit OFFLINE  


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Posted Sun Feb 18, 2018 11:39 PM

Please forgive my ignorance, but what is the difference between these? Why do the "Unidisk" models command such a higher price?

#2 H454 ONLINE  



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Posted Mon Feb 19, 2018 2:11 AM

Just a 1.44mb drive for the IIGS. But worked on IIc will the right ROM and IIE with the right drive interface card ( also expensive and hard to find).

I think that that its the one with the extra hardware ( like a its own cpu). I think its rare because IIgs were mainly bought by schools and they were NOT going to spend $$$ on a drive when 800k was fine for most people.

When I was a Kid (2-3 grade - 1992/93), The "computer lab"  had a room of IIgs that started off the HD connected to a couple of Mac SEs and we saved all of are stuff on them. None of the IIIgs in lab even had floppy drives.

That and I don't of anybody that had a IIgs as their home computer.

Plus, almost any software that wasn't made specifically for the IIgs, came on 5.25 disks.


This from the "DISK II" wiki pretty well explains the differences for those that don't know. (spoiler - Kinda of a Sh!t show).


In 1984, Apple had opted for the more modern, Sony-designed 3.5" floppy disk in late-model Lisas and the new Apple Macintosh. Accordingly, they attempted to introduce a new 3.5" 800k floppy disk format for the Apple II series as well, to eventually replace the 140k Disk II format. However, the external UniDisk 3.5 drive required a ROM upgrade (for existing Apple IIc machines; new ones shipped after this time had it from the factory) or a new kind of disk controller card (the so-called "Liron Card", for the Apple IIe) to be used. The much larger capacity and higher bitrate of the 3.5" drives made it impractical to use the software-driven Disk II controller because the 1Mhz 6502 CPU in the Apple II line was too slow to be able to read them. Thus a new and much more advanced (and correspondingly expensive) hardware floppy controller had to be used. And many original Apple IIs could not use the new controller card at all without further upgrades. Also, almost all commercial software for the Apple II series continued to be published on 5.25" disks which had a much larger installed base. All of these reasons added up to one thing: the 3.5" format was not widely accepted by Apple II users. The Apple 3.5 Drive used the same 800k format as the UniDisk 3.5", but it did away with the internal computer, which made it cheaper. Unlike all earlier Apple II drives, it was designed to work with the Macintosh too, and among Apple II models, it was compatible only with the Apple IIGS and the Apple IIc+ models, which both had a faster main CPU. On the Apple IIGS, whose improved audiovisual capacities really demanded a higher-capacity disk format as well, the 3.5" format was accepted by users and became the standard format. Though Apple eventually offered a 1.44MB Superdrive with matching controller card for the Apple II series as well, the 5.25" Disk II format drives continued to be offered alongside the newer 3.5" drives and remained the standard on the non-IIgs models until the platform was discontinued in 1993.

Officially, the following 3.5" drives could be used on the Apple II:

  • Apple 3.5" External (A9M0106) - Designed for Apple IIs with the Liron or Superdrive controller or all Macintoshes with an external 19-pin floppy port (Mac 512s must be booted from the internal 400k drive with the HD20 INIT, which provides HFS file system support - the Mac 128 will not work with this). The drive can be daisy chained, however this feature is not supported on the Macintosh.
  • Unidisk 3.5" Drive (A2M2053) - Designed for Apple IIs with the Liron or Superdrive controller (not compatible with Macintoshes) Recommended only for 8-bit Apple IIs as the A9M0106 operates faster on the IIGS
  • Apple FDHD External (G7287) - Supports 720k/1.44MB MFM floppy disks in addition to 800k GCR. Designed for Apple IIs and Macs with the Superdrive controller, but will also work on machines with the older 800k controller (as an 800k drive - note that the G7287 is not compatible with the Mac 128/512)

The 400k and 800k Macintosh external drives (M0130 and M0131) are incompatible with standard Apple II controllers as they do not support their automatic disk eject feature, although they could be used with third-party controllers."

#3 c0op3r OFFLINE  


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Posted Mon Feb 19, 2018 7:30 AM

Unidisk is a slow piece of shit - dont bother.  get a regular AM106 3.5 you can get them for 15 to 25 all day on eBay.  Order some of the replacement eject gears as there is a good chance it will be broken or will break soon.

#4 eightbit OFFLINE  


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Posted Mon Feb 19, 2018 12:49 PM

Good info. Looks like I'm not missing much then. Already have a good working 3.5 drive. Thanks for the info folks!

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