I recently acquired an Apple IIgs with two 3.5" floppy drives and no hard disk. I'm very seasoned with older Macs, but I have no experience within the Apple II world.

I search for a way to create floppies to be used with that machine with help of an an older Mac: Both machines use the 800k GCR format.

The Apple II Documentation Project has a number of Disk Images for download, most often in .po format. (I learned that the other format, .2mg is used with Emulators.) These usually have 819,200 Bytes. According to this source, this is a .hdv-image type:

.hdv- typically an image 800k (819,200 bytes) or greater in size in ProDOS order. The image is intended for use as a virtual hard disk by various Apple II and IIgs emulators (e.g. Apple Oasis). The IIgs program ASIMOV2 can create .hdv files (select "Raw image"). The file name should end with ".hdv".

The bold emphasized text suggests that this is a binary image, about the same when reading a floppy disk in a PC with Linux with dd and writing the output into a file.

I did even more research here, here, and here. Some of these sites more or less silently assume a hard disk on the IIgs, or even using an emulator. All in all, the described procedures seem to be very cumbersome.

Is there any easy way (like just changing the Macintosh file type code?) to write these .po images to 800k Floppy Disks with just DiskCopy on an older Mac?

  • Boo, under the what won't work: I had remembered reading that folks were able to send stuff via audio (basically, older apple's supported reading cassettes in addition to disks) ... but per adtpro.sourceforge.net/bootstrapaudio.html, Apple IIGS doesn't have that option ... I think technically if you knew someone with an Apple IIE and a 3.5 drive, they could do this and then you'd have a serial program you could use to then copy stuff over serial... but I'm not seeing a way to get around for bootstrapping
    – Foon
    Commented Apr 2, 2021 at 21:34
  • 1
    (though adtpro.com/bootstrap.html#Starting_from_bare_metal makes it sound like you could bootstrap... but then the next issue is getting the appropriate cable), but that might be doable (and then you can use vanilla modernish stuff as the host vs using an older mac which is the focus of this question)
    – Foon
    Commented Apr 2, 2021 at 21:38
  • Not necessarily helpful: 2MG is usually just a PO with a header. The header can identify a different internal format but PO-wrapping 2MGs seem to be far and away the most common.
    – Tommy
    Commented Apr 3, 2021 at 21:35
  • @Foon - the serial cable bootstrap works well, and I've used it to create IIgs floppies with no other old Apple machine available
    – scruss
    Commented Apr 3, 2021 at 21:41

1 Answer 1


It is rather straight-forward, technically speaking, to share both 3.5" floppy disks and their image files between a Classic Mac (e.g. MacOS System 7) and an Apple IIgs. This because both systems support ProDOS floppies and HFS floppies (in GS/OS), and both systems support image files for 800KB disks using DiskCopy 4.2. So, that solves most needs back in the day.

Since you are retrieving IIgs files in the .po (ProDOS Disk Image) format, you are introducing a "wrinkle". I think this is best solved using CiderPress, which is a pretty capable disk image file manager for Apple II disks that happens to run on Windows XP (and higher).

CiderPress can be downloaded and installed on a Windows machine, and your .po image files easily opened with it. There is also a tool within CiderPress called Disk Image Converter. It is this converter tool that is able to export the 3.5" ProDOS .po images as Disk Copy 4.2 .dsk image files. Those files can then be transferred to a Mac where you can, in theory at least, write them to actual ProDOS floppies that will work on the IIgs.

A simple way to convert the .po to .dsk images on the Classic Mac would be preferred, obviously. I don't recall whether it works, but you could try just changing the resource fork, and see if they open directly on the Mac with Disk Copy 4.2.

ADTPro is also worth considering. With the simple addition of a serial cable between the IIgs and your modern machine, you can write the .po files (on the modern machine) to the floppy disk connected to the IIgs. This is actually my preferred way to create 3.5" floppies from images on the IIgs.

  • 1
    While there seems to be no existent program to just use a Mac, CiderPress is better than nothing. Since it's available as source code, it may be feasible to just extract that code to have a command line utility without Java Requirement. Together with Netatalk, setting the proper type "dImg" and creator "ddsk" codes would ease-up transfers even more. github.com/zellyn/diskii shows a lot more utilities, maybe what I dream of is already there.
    – PoC
    Commented Apr 4, 2021 at 10:14
  • Renaming Files on a Mac does nothing. Old classic MacOS' use a "hidden" means of type and creator codes to know if they should even try to open a file, and which program to launch when double-clicking a file. My preferred way of editing is FileTyper, small and lean.
    – PoC
    Commented Apr 4, 2021 at 10:18

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .