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Mad With Macintosh


Running Mac OS 8.5 on A 68k Mac with A PPC Upgrade Card


Running MacOS 8.5 on a PPC upgraded Performa 475 Posted 10/24/1998

Monday morning update (10/26/98) … this may be trickier than I thought for
some machines. I was in contact with a guy Sunday afternoon who was
installing on a Mac IIci w/ TurboPro 601/100. We never did get the right
Gestalt mach id number.

I also heard from an experienced Mac user who warned of potential problems
and constraints: can't boot from CD, more likely to have software
incompatibilities, lack of support from Apple or other SW manufacturers.

On the positive side, there are two references from those have been able to
install on "unsupported" machines.


8.5 on PowerBook 540 w/ PPC Upgrade

8.5 on Quadra 700 with PPC Upgrade

Yes it can be done!!

Here's what Apple says in "Installing Mac OS 8.5" on the 8.5 install disk:

"• Computers with PowerPC processor upgrade cards

You cannot use Mac OS 8.5 on a computer with a 680x0 processor that has been
upgraded with a PowerPC processor upgrade card."

Thanks Apple, now here's how Bob says you CAN do it ...

Note: I have only tested this on a PPC upgraded Performa 475. It should work
on other 68040/PPC upgrades. It might even work on 68030 TurboPro machines.
The same concept may work on G3 upgrades that do not install MacOS 8.5.
(This is a work in progress. I'll add hyperlinks when I get more time.
Contact me with suggestions at Robertotec@aol.com. )


1. It is best to do this on a separate hard drive from your startup drive.
You should at least use a volume other than your startup volume.

2. Make sure your drives are backed up.

3. Don't hack anything with a Resource Editor that you can't afford to lose.
That usually means to work only on copies of files.

4. If you are using separate volumes on the same hard drive, you will need
System Picker or System Switcher to let you switch between Startup Folders.

5. Determine the 'mach' gestalt number of your upgraded system. You can use
Techtool or Apple System Profiler to determine this. You will need to
convert this number from decimal to hex. Or see Table 1. at the end of this


1. Fool the installer into thinking that you are installing on a compatible

2. Install 8.5 on your selected drive.

3. Edit the new 8.5 System file so that it will recognize your computer as a
compatible machine.

4. Remove/replace Extensions and Apps that are not compatible.

5. Test out your new system.

6. Update your utilities and apps to 8.5 compatible versions.


1. Fool the installer

Get a copy of Wish I Were ... and install it on your current system.

Restart, set the Wish I Were ... control panel to a system similar to your
upgraded system. (I would suggest a 6100/66, 7100/80, or 8100/100.) Restart

2. Install 8.5.

Install on another drive or at least a separate partition (volume). It
should install if you have Wish I Were ... set right. At this point you
could try to restart with the 8.5 Startup Volume, just to prove to yourself
that it will not work. You will get an error message as soon as the startup
screen shows up.

3. Use Resedit or Resorcerer to open the 8.5 System file.

Open the "gusd" resource, open resource 1. Locate the values 001F 001C.
Replace the 1F with the mach gestalt number for your machine in hex. (For my
system it is 104 decimal which converts to 68 hex.) [HELP! What is the
second number? The 1C is related to the type of processor. It doesn't seem
to correspond to any of the Gestalts that I am aware of. The Q700 used 16
instead of 1 C, though both are PPC601's.]

4. Remove/replace Extensions and Apps that are not compatible.

Check the Extensions folder and remove IOmega Driver 6.0.1. I found that to
be incompatible. I also found Apple System Profiler 2.1.1 would hang up if I
selected "Devices and Volumes".

5. Select the OS8.5 System Folder as the startup folder. Restart with
Extensions off (hold down shift key during restart). It should start up in
OS8.5. Restart normally and see if you crash. You may have to check out your
Extensions by trial and error using Extensions Manager.

6. Check Version Tracker to see what Utilities and Apps you need to update.

Table 1. Machine ID: mach Gestalt numbers for Upgraded Machines

Hex, Dec, Upgraded Machine Name

68, 104, PowerMac LC 475/Performa 47x (This may also be the gestalt for all
100mhz 601 upgrades.)

69, 105, PowerMac LC 575/Performa 57x

6A, 106, PowerMac LC-Quadra 630/Performa 63x

6B, 107, PowerMac LC 580

74, 116, PowerMac Quadra 700

75, 117, PowerMac Quadra 900

76, 118, PowerMac Quadra 950

77, 119, PowerMac Centris 610

78, 120, PowerMac Centris 650

79, 121, PowerMac Quadra 610

7A, 122, PowerMac Quadra 650

7B, 123, PowerMac Quadra 800

7E, 126, PPC PowerBook 520-540

CE, 206, PowerMac IIci

CF, 207, PowerMac IIsi

D0, 208, PowerMac IIvi

D1, 209, PowerMac IIvx

D2, 210, PowerMac IIvm

D3, 211, PowerMac IIfx

You can contact me at Robertotec@aol.com

Bob Rabun

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