Classic Mac Hardware (Troubleshooting, Upgrading, & Modifying) > Mac CPU Upgrades

Swapping CPUs Between Two MDDs

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ObiWanCanOweMe:
So I've got two MDD Power Macs:

1. Apple Power Macintosh G4 1.0 DP (MDD) - https://everymac.com/systems/apple/powermac_g4/specs/powermac_g4_1.0_dp_mdd.html
2. Apple Power Macintosh G4 1.0 (FW 800) - https://everymac.com/systems/apple/powermac_g4/specs/powermac_g4_1.0_mdd.html

MDD #1 can boot OS 9 natively and #2 can only boot OS 9 using MacOS9Lives.
Is it possible to swap the CPUs so that the DP goes in #2 and the SP goes in #1? I'd like the OS 9 machine to have a SP and the OS X machine to have DPs

Thanks!

FBz:
You might want to check the bus speed of both machines to determine if they’re 133 or 167 MHz and if they’re the same - that’s a nod to test it for certain. EveryMac.com notes that the 1.0 FW 800 machine has 133 MHz, while it also notes the DP 1.0 GHz DP machine as having a bus speed of 167 Mhz. Both machines have the 300 pin daughtercard mounted CPUs.

https://everymac.com/systems/apple/powermac_g4/specs/powermac_g4_1.0_mdd.html

https://everymac.com/systems/apple/powermac_g4/specs/powermac_g4_1.0_dp_mdd.html

There is possibly a resistor than can be removed from the FW 800 machine’s mobo (if it’s throttled to 133 MHz) that might increase its’ bus speed to 167 MHz. But first I would determine if the swap works well for both, before I’d remove that resistor.

I have moved faster 1.42 GHz DP FW800 CPUs into “lesser” FW 400 machines with tested success - but they were both 167 MHz mobos (and in some cases, 133 MHz bus speed mobos with the aforementioned single resistor removed). So I can personally attest to “backwards compatibility”. It’s the “forward move” of your dual CPU that I have not personally tested. But I’m guessing that it will work. (That guessing always makes one feel more confident.)

If it boots, then check “About This Mac” / More Info to see what bus speed the FW800 machine reports afterwards. (Again as first suggested here, check this before any CPU moves.) After the moves, and (hopefully) successful subsequent boots… check again to see if you may want to snip that resistor as the CPU may report slightly less than 1.0 GHz?

Resistor and 1.42 CPU swap… thread: http://macos9lives.com/smforum/index.php/topic,6285.0.html

And P.S.  You may need to reset the PMU(s) after the swaps & ZAP the PRAM on both machines. ;)

GaryN:
No, this is not confusing at all…

ObiWanCanOweMe:
Thank you VERY much for the response and suggestions. Pretty much exactly what I was looking for and I did not find it at all confusing.
I've been reading a lot of forum posts regarding CPU upgrades so this jives with what I've seen. It is much nicer to get a summary from a single source though  :)
I'll check the bus speeds and report back with my progress.

ObiWanCanOweMe:
So the DP is 167 MHz and the SP is 133 MHz. I'm going to try the swap. Are there any guides or directions you'd suggest I follow for the actual process of removing and remounting the CPUs? I've been building PCs for years but never done anything like this on a Mac.

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