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Ask Max: Trouble while option booting upgraded PowerMac G4

Asked on 04/11/2007:

Back in January 2006 I installed your 1.5 GHz upgrade for my 400 MHz PowerMac G4. As far as I know, everything has worked properly ever since.

However, today I discovered an anomaly that nobody can explain, and someone has suggested that it might somehow be related to the CPU upgrade, or to the firmware upgrade to Version 4.2.8f1, that I had to install first:

If I attempt to boot my machine while holding down the Option key, so that I can select the desired startup disk on the fly, I see the following text message:

"ALL -MEM request too big!Apple PowerMac3,3 4.2.8f1 BootROM built on 10/11/01 at 14:12:47"--- copyright and welcome to Open Firmware ---"To continue booting, type "mac-boot" and press return.To shut down, type "shut-down" and press return."

If I enter "mac-boot", it boots from the default drive without giving me a chance to make a selection. However, I can boot and run from either the default or the backup drive if I select one of them from the System Preferences Startup Disk dialog, and then reboot.

Have you ever heard of this problem before? Do you think that it could have anything to do with my ROM or CPU upgrade?


There is a small boot-loader that lives in modern Macs' firmware and that is what you see when you hold down the option key. It's possible that your processor upgrade scrambles the low-level software that is needed to run the boot-loader. It is of course written for a different processor than what you are running it on. When firmware crashes, it takes you to the command line you described. A test you could try is holding down the "T" key to see if the G4 can go into a target disk mode. The boot-loader and target disk mode are similar in how they communicate with hardware.

Also, if you still have your old processor, you could put it back in and see if that makes a difference. After that, make sure that the firmware install was fully successful.

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