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Downgrading from Mac OS 8.1 to 7.5


Well-known member
Us simpletons sometimes don't realize we are simpletons and ask questions on message boards.

I was going to post another thread entitled "Where do I plug my Xbox 360 controller into my Mac Plus" but I caught myself.

With the proper adapter, its certainly possible!

I finally got it working.


1) Boot with 7.5 Network Access Floppy Disk or Disk Tools

2) Insert Drive Setup (IDE) CD (burned)

3) Delete 1GB partition and format

4) Reboot with 7.5 Floppy Disk

5) Insert 631CD Restore with 7.5.1 and Install

6) Install 7.5.3 update on CD (burned)

7) Install 7.5.5 update on CD (burned)

Luckily this model has a CD-ROM drive that reads ISO 9960 ok or I would have been up the creek, or buying more accessories on eBay.

Elfin: you are correct, 24bit addressing is not supported on this model, which I found out after install.  Unfortunately, Lowend Mac and other sources reports that it does support 24bit.

I'm much happier with 7.5 over 8.1.  Even with no 24bit addressing, compatibility with older software has been much improved.  Plus the System and Finder only take up 3.5MB of RAM instead of 8.5MB under Mac OS 8.1.  

My only complaint is that 7.5 won't read Multi-Session CD's and 8.1 will.  So that means I have a bunch of CDr platters with empty space since I can't reuse the discs. 



Maker of Logos
Just a tip: You totally can re-partition a drive while keeping the data... not sure why anyone said otherwise. Boot Linux up on a livecd with the hfsprogs package and GParted. Piece of cake. At worst you have sticky partition header positioning, which can be fixed by imaging.

Last edited by a moderator:


New member
Sorry for the thread necromancy, but this is the only discussion I've seen where someone reported success with gparted.

Floofies, or anyone else:

Did you actually have success using gparted to resize HFS partitions on a 68k Mac? Firstly, linux live cds for 68k Macs appear not to exist. All installation methods both for linux and netbsd involve a bootloader launched from Mac OS (Penguin or similar). Secondly, there's not a modern distro that support 68k - Debian "revived" its 68k port in 2012, but the last official releases are from 2009. This is not going to have a recent version of (g)parted. GParted live cds are for x86(-64) only. Finally, people have reported issues with the apple partition map after using gparted to resize (report was on ppc).

I, and I'm sure others who will come across this later, need to know whether a) you have successfully done this and, if so, with what "live cd" or b) you were speaking in theory (it ought to be possible), or confused the case of doing it on a modern x86-64 "Mac" with doing it on a 68k classic Mac.



Well-known member
Yea, so much bad info on this thread it should be noted.
Certainly 68k Macs will not boot with hfs+ formatted disk.
With Mac O 8.1 installed and booted on an hfs disk on a 68k Mac the Finder can use hfs+ disks and partitions but cannot boot from them.
So if the Macintosh Performa 631CD OP has was running Mac OS 8.1 it was doing so from a hfs formatted disk. I do the same with my SE/30.
There is no need to format the drive to put Mac OS System 7 on it. I have both installed on the same drive and use System Picker to switch between them.