G4 processor upgrade question

[Powertrip]

So back in the day when I got my collection of college macs, I got several 733MHz Quicksilvers and several 400MHz gigabit models. The GBs all had Gigadesigns 800MHz upgrades with 2MB cache.

Now I am going from memory but I recall swapping the upgrade CPU from a working GB to a working QS but could not get it to boot. No chime, nothing (that I recall).

Now my question is, if I try to put another of these in my remaining maxed out 733MHz QS, should it in theory just be a case of reset PRAM/NVRAM regimen or is there something else I do not know about the upgrades?

Thanks! (I am slowly working through my collection to trim down to working machines only).

 

[Elfen]

Read over:

http://www.jcsenterprises.com/Japamacs_Page/Processors.html

 

[Powertrip]

I did, but that seemed mostly to discuss the difficulties of OEM processors versus aftermarket upgrade and whether those were made compatible between my two generations.

ETA:

It seems like an upgrade was made to work with a Sawtooth that was originally for a QS but had to do some software tweaks.

 

[Elfen]

The 2 biggest problems you will have is the CPU Socket, heat sink fitting and Logic Board Bus Speed vs CPU MHz. Yes, I did say 2... It's that funny 1990's math.

Many of the G4 groups share the same CPU Socket, even the Dual CPUs on a single socket. But the problem is the heat sink fitting as the CPU is on a board and the board on a socket and it fitting on the socket, the CPU can be in a different location on the cared portion of the device. This would make fitting the Heat Sink an issue.

A lot of the G4s are tied up in Logic Board Data Bus Speed groupss, despite the CPU speed. 66MHz (on the old G3s), 100MHz (on faster G3s and first G4s), 133MHz, 166Mhz, and so on... are where various G4 models are in. If the DataBus speeds does not match despite the G4's transplanted MHz, at best the Mac turns on, boots but runs slow or not as fast as one expected; at worst, it won't boot at all or even turn on.

EDIT: What you are proposing is something of a jump that is going to cross the second problem - Databus Speed, even if you can pass the first step. The question is, will it run? I don't know personally. But if the CPU Socket fits, it should. If it turns on, it just might. But with the slower databus speeds of the logic board with a faster CPU, it may not run as fast as you think it will.

EDIT 2: Read the link again; but go to the Mirror Drive Door section... They discuss this there and a possible "fix."

 

[waynestewart]

Almost all the aftermarket processors that work in any of the G4 QS, DA, GE or Sawtooth will work in the rest. Usually you have to set some jumpers, switches or a dial to set either buss speed or processor speed

 

[Powertrip]

Thanks for the input, guys.

 

[Elfen]

WayneStewart - You are very much right with the third-party and aftermarket G4s. Those G4s have adjustable or "tunable" Databus Speeds. Stock Apple G4s do not and are fixed with what they are set too, with the exception of a tiny few one can move a SMT/SMD resistor to change the databus clock speed. So one is limited in what one can do with Stock Apple CPUs. But this subject is interesting though.

Somewhere I heard of some people doing the same thing with G5s, swapping out a 1.8GHz with a 2.2GHz or 2.5MHz.

 

[waynestewart]

The G5s didn't allow you to make any processor upgrades. You could swap in the identical processor from the same year but that was it.

 

[johnklos]

Some G4 accelerators with, I believe, PowerPC 7457 processors require a firmware update to run. Others with 7447a / 7448 processors require a firmware update AND require the PRAM be configured properly, so that a PRAM reset will make the system non-bootable. Here's an example:

http://www.newertech.com/downloads/nwtmang4max.pdf

 

[Unknown_K]

Apples seemed to custom design each G5 motherboard to the CPU or something crazy like that.