Sidebar Sidebar
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.

G4 processor swap issues

TheMasin9

TheMasin9

macrumors 6502a
Original poster
Dec 22, 2004
585
0
Huber Heights, OH
i have a couple of power mac g4s around the place and i recently swapped some of the processors around. I originaly had a pair of g4 466 "digital audio" machines and a g4 400 "sawtooth". After moving them around i end up with with a 466 "digital audio" a 533 "sawtooth" and a 350 "digital audio" can anyone tell me what is up with this. Does it have to do with the bus speed?
 
It has to do with the processor multiplier. Basically each CPU has a different "default" processor modifier, so when you move it to another machine (with a different multiplier configuration) it makes the CPU go faster/slower.
 
The sawtooth and DA did have different bus speeds- the DA was 133, while the sawtooth was 100. This should have nothing to do with the CPU swapping, but rather the type of RAM stick that might be useful to you.

Now this is weird... One thing I was going to ask was whether you were sure that those CPUs were swappable. I know that they use different PSU adaptors- i.e. the sawtooths used the 20 pin adaptor, while the DAs had the weird 22 pin adaptor. Adding 50 Mhz from one chip to another makes no sense, and it might be that you've fried something.


EDIT: Ah- crazyeddie got it. My bad.
 
I would guess the bus speed is the cause. The Sawtooth had a bus speed of 100MHz while the DA was 133MHz. The processors speed is determined by multiplying the bus speed.
 
Lovesong said:
The sawtooth and DA did have different bus speeds- the DA was 133, while the sawtooth was 100. This should have nothing to do with the CPU swapping, but rather the type of RAM stick that might be useful to you.

Now this is weird... One thing I was going to ask was whether you were sure that those CPUs were swappable. I know that they use different PSU adaptors- i.e. the sawtooths used the 20 pin adaptor, while the DAs had the weird 22 pin adaptor. Adding 50 Mhz from one chip to another makes no sense, and it might be that you've fried something.
Click to expand...

Processors swapped no problem, plug in plug out, they all have that ziff socket (i believe that is what its called).
 
Lovesong said:
The sawtooth and DA did have different bus speeds- the DA was 133, while the sawtooth was 100. This should have nothing to do with the CPU swapping, but rather the type of RAM stick that might be useful to you.
Click to expand...

It has everything to do with the bus speed and the multiplier set on the motherboard or daughtercard. The G4 processor can run at half integer multiples of the bus speed. Some motherboards/daughtercards allow you to change the multiplier.
 
I think we can do a little math to figure it out. Lets take the example of a processor swap between a 466 DA and a 400 Sawtooth.

Sawtooth: 100Mhz bus x 4.0 multiplier = 400Mhz CPU
DA: 133Mhz bus x 3.5 multiplier = 466Mhz CPU

Now, a 100Mhz bus sawtooth G4 can't or won't operate at 133Mhz bus speeds. That means the DA must have clocked itself down to 100Mhz bus, but applied the original 3.5 multiplier. This would give you 350Mhz on the DA.

The Sawtooth machine is more of a wonder. It appears it adjusted appropriately to the 133Mhz bus of the newer CPU, but applied its old multiplier as well. 133Mhz x 4.0 multiplier = 533 Mhz. What I don't understand is how the Sawtooth appears to operate at that bus, given the motherboard RAM speed limitations, etc. It could be a false finder reading, perhaps.
 
You must log in or register to reply here.
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.
Top Bottom
Back