Installing “Unsupported” Software on an Overclocked LC 475
(Or more generally, installing software on any unsupported classic Macintosh)
You might find that if you have overclocked your LC 475, Performa 475, Performa 476 or Quadra 605 by moving the speed selecting resistors on the underside of the board, you can no longer install some operating system versions, including Mac OS 8.1 for example.
The reason for this, is that the machine id gestalt, effectively the number representing the computer model from the operating system’s perspective, changes when you change the computer’s speed in this way. When you launch some System installers, they check the machine id gestalt, and some, but not all, don’t include the id for a 33MHz LC 475 type computer.
There are three easy solutions for this, depending on your exact needs…
Try Forcing it to Install
Some Apple Installers will ignore the machine check if you hold down the opting key while launching the software. Note this unfortunately doesn’t work with the Mac OS 8.1 installer, but it does work with some older Apple installers. To do this, you can hold it down prior to double clicking, but make sure you keep it held down through the dialogue boxes until you get to the one that lets you pick your install type. At this point, remembering that the installer doesn’t have an appropriate profile for what it thinks your computer is, select “Universal System for any Supported Computer” to make sure everything that is needing gets installed. Note this will be a bigger system install than you really need as it will include all sorts of machine specific extras and even probably PPC code, that your specific computer likely doesn’t need.
Override Your Machine ID
It is possible to set your Machine ID Gestalt in software and there are a couple of different tools for doing it. The most famous one is “Wish I Were”, but for this specific job, it isn’t actually the best choice. Wish I Were is great if you want to change your machine ID long term as it changes it fairly early in the boot process (not early enough if the OS doesn’t support the computer at all, but that isn’t an issue here).
On the other hand, the software “MachID Wannabe”, available here from Macintosh Garden : https://macintoshgarden.org/apps/wannabe-macintosh lets you instantly change your machine ID and it only stays changed until you change it again or shutdown / restart. This is great as without restarting you can change it, then run the installer, and get on with your life. You do still need to install MachID in the Control Panels folder and restart to be able to use it though!
If you’re trying to make an LC / Performa 475 or 476 appear stock, you’ll want to set it to 89. A Quadra 605 would be 94. It doesn’t really make a difference which of these two you pick.
Put the Resistors Back
The third and final option is to just put the resistors back to the default configuration, and instead, install my software overclock Control Strip Module. The module lets you change the speed between more configurations and on the fly. Because the resistors are in their default position, the computer retains its stock Machine ID Gestalt and all installers, software and OSes that check the machID get the expected value for an LC 475, maximising compatibility. I might be bias, but this really seems like the best solution to me!
The latest version can be found here on Macintosh Garden : https://macintoshgarden.org/apps/control-strip-475-overclock
Useful Information
For information about overclocking an LC 475 or related computer, or many other classic Macs, as well as useful information about the machine ID gestalt (commonly called just “gestalt”, although technically the machine ID / machID is one of many gestalts), please check out the amazing http://applefool.com, and specifically http://appplefool.com/clockchipping/.
If you want to know more background about the software overclocking method, check out my post here, and the original 68kmla forum thread by mustermann here.