I have noticed that the fastest single G4 CPU module board for the MDD G4 PowerMac's and Xserve, PowerMac rack mount servers appears to be a 1.33GHz G4 model.

I am wondering if anyone has seen any information about overclocking the 1.33GHz G4, as opposed to the 1.25GHz G4 for use in the MDD G4 PowerMac? Just wondering if the 1.33GHz G4 CPU module is a better overclocking candidate than the 1.25GHz G4 CPU module?

I have purchased one of the single 1.25GHz G4 CPU modules with the intent of overclocking it to 1.5GHz and using it instead of my dual 1.42GHz G4 CPU module, so it will produce less heat and need less cooling effort, which will hopefully mean less fan noise while running an overclocked G4. I have already replaced my noisy main CPU heat sink fan with a so-called "Silent" fan, and I was considering replacing the PSU twin fans, with less noisy ones, but after I checked the noise level of these fans at full voltage and speed, I realized that they were very quiet and did not need to be replaced.

Since MorphOS can only use a single G4 CPU and I have a G5 PowerMac and an Intel MacMini to run MacOSX, I do not need dual 1.42GHz G4 in my MDD to run MacOSX more quickly in a dual boot setup, and can dedicate my MDD to MorphOS alone.

I should probably have just e-mailed David, but posting a response will serve double purpose.
David and I have discussed this idea and I too have purchased a single 1.25 GHz G4 processor card.
David has the information to change the multiplier on these cards, but no one seems to know how change the voltage.
As dual processor Xserve cards use the same layout a standard MDD dual processor cards (and the voltage and multiplier resistors are known for these) I've also purchased a 1.33 GHz Xserve processor card. Xserve processor cards have twice the L3 cache, so in theory, at the same clock speed an Xserve processor should be more powerful then a standard MDD processor.

I'm pretty sure we can get the single processor cards to run at 1.42, but without a voltage mod, 1.5 GHz may prove problematic.
I believe I can get the Xserve processor card to run at 1.5 GHz, but the heat generated by two CPUs will be fairly high.

Ideally, a single CPU 1.33 Xserve processor with multiplier AND voltage mods would probably perform best.
We might even be able to push this above 1.5 GHz using the copper heatsink from a 1.42 GHz dual processor FW800.

So, what we need is information on modifying the resistors that control voltage and multiplier settings on Xserve single processor CPU cards.

A 1.42 GHz 7455 is already about as powerful as a faster 7447. But as Redrumloa's benchmarks have proven a fast 7448 is even more powerful. But 7448 processor cards are usually quite expensive.
Overclocking these Xserve processors, under MorphOS, may be a low cost way to maximize our performance.

You are much better an explaining things than I am.

I was not aware that you had purchased an Xserve G4 CPU module? From your posting though, I assume it is the dual processor version, and not a single G4 CPU module (wonder if they even made a single G4 CPU module for the Xserve? Thought I saw one advertised, but can't be sure of my memory).

> wonder if they even made a single G4 CPU module for the Xserve?

http://www.everymac.com/systems/apple/xserve/specs/xserve_g4_1ghz.html
http://www.everymac.com/systems/apple/xserve/specs/xserve_g4_1.33.html
http://support.apple.com/kb/SP72
http://support.apple.com/kb/SP102

The problem is the L3 cache ram, which is limiting the possible overclocking values of the 7455 cpu modules.

Tom01,
Quote:

Can you provide your source for this information and provide any further details on your experience with overclocking the G4 PowerMac's?

Share with us what you think is the best G4 CPU module for overclocking and MorphOS use. At first I assumed that the single 1.25GHz G4 CPU module might be the best candidate for overclocking and using for MorphOS alone, but I am not so sure anymore.

Tom01,
Quote:

I doubt the Xserve's L3 cache will be any bigger a limitation then the standard FW800's 1MB L3 Cache.
Since dual processor 1.25 and 1.42 GHz processor cards easily overclock to 1.5 GHz, its a fair assumption that the Xserve 1.33 GHz processors will too.

I intend to modify the dual processor Xserve card as soon as I get it and test it at 1.5GHz.

The real trick will be getting the single processor cards to overclock (as I've mentioned we don't know how to up the Vcore).
However, as I also mentioned, with only one processor we should be able to use a higher Vcore while still providing adequate cooling.

As soon as I get the first processor up and running I'll try to provide benchmarks that can be compared to Redrumloa's.

Quote:

Jim are you looking for Vcore spec for Xserve single cpu card or for MDD single 1.25 ghz one?
If the answer is the number two, take a look here:
http://aquamac.proboards.com/index.cgi?board=talk&action=display&thread=767

Looks like some good info though, thanks for the link. I have not had a chance to look at all of it. Reading some of the forum posts there and the benchmarks/test results, it appears that overclocking a single 1.25GHz G4 CPU up to 1.5GHz, or 1.58GHz should be stable.

That is more than enough for my satisfaction. It will put my MDD a bit ahead of my 1.5GHz G4 MacMini and close to the same clock speed as my 1.67GHz G4 PowerBook's.

I realize that there are other factors besides just the clock speed of the G4 that determines performance, but it will be interesting to compare all three of these G4 Mac models, once the overclocking is completed.

Do the Xserve G4 CPU modules have twice the L3 cache that the MDD has (2mb opposed to the MDD's 1mb)? Do the single G4 CPU modules have the same amount of L2 & L3 cache as the dual G4 CPU modules?

>Do the Xserve G4 CPU modules have twice the L3 cache that the MDD has (2mb opposed to the MDD's 1mb)? Do the single G4 CPU modules have the same amount of L2 & L3 cache as the dual G4 CPU modules?

Andreas already posted a link confirming that.

http://support.apple.com/kb/SP102

The real question is are the Vcore resistors the same on MDD and Xserve single cpu boards?

[ Edited by Jim 06.05.2012 - 01:05 ]

Well, I have both CPU cards on hand now, but thanks to Jambalah I'm going to try the single 1.25 MDD processor first.
If I'm lucky I'll get it to run at 1.67 GHz.

Now that I have been successful in fixing a few of my other computer problems, I hope to have some time to look at the most recent links provided by a few other members here and elsewhere that mention other MDD PowerMac owners being successful in overclocking their single 1.25GHz G4 CPU modules up to 1.67GHz.

It will be great if we are successful in getting that speed out of the single 1.25GHz G4 CPU modules and still have a stable system that is not over heating.

Jim,
Quote:
OK, that's strange as the FW800 I've just got reported 2MB L3 cache, and I looked at that at two different points before zapping the HD with MOS, but that's what EveryMac say too. Does that mean I must have the processor card from one of these?

>> the standard FW800's 1MB L3 Cache

> that's strange as the FW800 I've just got reported 2MB L3 cache

I think he was referring to the per-CPU amount of L3 cache. According to this thread, you have a dual-CPU 1.25 GHz FW800 which means that what you got reported should be fine.

> that's what EveryMac say too.

That site also lists the per-CPU amount of cache, so the dual-CPU 1.25 GHz card from the non-FW800 MDD should have 4 MiB L3 cache in total, as has the dual-CPU 1.42 GHz card from the FW800 MDD btw.

Thanks Andreas,
That was my assumption till you pointed out the two models that have 2MB L3 per CPU (which curiously enough included my own).

Ah I see, that makes sense, thanks.

Just for a quick info. Single CPU card for MDD overclocked from 1.25 to 1.67Ghz (with increasing voltage to 1.65V) works fine (so far) under MorphOS but OSX is unstable.

Thanks Pampers,
I haven't had time to modify any of the CPUs I've got on hand (its been a really busy month).
So its nice to know which I ought to start with.

So far so good with open MDD at 1.67 as stock cooling system is too weak to handle it. Will be looking for some other cooling or I will downclock it back.

I can sympathize.
My 1.42 GHz FW800 runs quite hot with a 9800XT video card installed.
I'm also looking at alternative cooling.

Dual 1.42 gets as hot as hell, about 60-62 degrees in here sometimes. That's why I've switched to a single cpu card as I won't be using osx too much.

@pampers,

Could you email me complete step-by-step process on how to over-clock the single 1.25GHz G4 CPU module for the MDD PowerMac up to 1.67GHz?

Or post the instructions here in this thread?

You mentioned that you increased the voltage, but did not make it clear how you did that, or if that was the only thing you did to increase the clock speed of your 1.25GHz G4 CPU module, to reach the clock speed of 1.67GHz.

I have the soldering skills to do the work myself, but have not been able to figure out the exact steps to take, to do the over-clocking on a single 1.25GHz G4 CPU module, to get it to the 1.67GHz clock speed.

All the information that I have found has only been for dual G4 CPU modules.

Edit: I also wonder how you are cooling the G4 CPU and heatsink with the case open, as that takes the heatsink out of the path of the main fan. I guess you probably have some other fan pointed at the G4 & heatsink. Are you using the stock Copper heatsink that came with the dual 1.42GHz G4 FW800 PowerMac? It was my hope that the single 1.25GHz G4 CPU over-clocked to 1.67GHz could be cooled enough with the stock Copper heatsink and fan from the dual 1.42GHz G4 FW800 PowerMac.

[ Edited by amigadave 27.06.2012 - 11:09 ]

@Amigadave:
post #8... I guess you forget.. doh!
Link takes to webpage with instructions for overclocking single 1.25 cpu modules.

@Jambalah,

I will check all the links again, but everything that I found was only for dual G4 CPU modules. Either that, or it did not include complete instructions on how to get the single 1.25GHz G4 CPU module up to 1.67GHz.

I must have missed something.

Edit: (typo mistake)

[ Edited by amigadave 27.06.2012 - 19:23 ]

Amigadave, Jambalah gave you the proper source with pictures of a single CPU board, the same thing you can find here:

http://www.mactalk.com.au/10/49293-overclocking-powermac-mdd.html#post725112

So basically with these pictures you've got explained what is where on a single card and then you can use tutorial from:

http://bitsandpieces.info/Multipliers.htm

That's it, not a big deal :)