Top End G5 an overclock?

[MikeLaRiviere]

Look at the Intel Analogy

A fact I believe no one has yet mentioned is that Intel experienced greater heat when it moved to the 90 nm technology. For example, the P4 3.0 is based on the old technology; the P4 3.0 Prescott is based on the 90 nm process. The Prescott, testers have found, leaks more heat than the Northwood (the older technology), even at the same clock speed. Because chips are now manufactured at 90 nm, heat leaks far more readily.

My guess is that the G5 2.5 processors are not overclocked, but that the 90 nm process in these IBM chips simply requires liquid cooling. I can't rule out the possibility that the 2.5s are overclocked; however, I would have to think that Apple would favor stability over higher advertised clock speeds. As we all know, and as someone in this thread has previously pointed out, clock speed is not the sole determinant of how "fast" the processor will run. Those of us who use Macs know this fact very well.

If there are any objections to/problems with my post, I welcome the replies.

Mike LaRiviere

 

[ddtlm]

MikeLaRiviere:

However since the 90nm P-M actually uses less power than the 130nm version, I think we can conclude Prescott is just a very poor design. Everyone is still left wondering what on earth all the transistors in there are doing.

 

[MikeLaRiviere]

Pentium M?

ddtlm, were you talking about the Pentium-M? I didn't know the M was on a 90 nm process, but then again I haven't been following this line closely. I am, however, impressed with the M line's performance.

The Prescott, in fact, uses more power than the Northwood, if I understand what I read correctly. I think you concur with this fact.

But this is beside the point; I don't imagine the 2.5 GHz G5 is overclocked.

Mike LaRiviere

 

[Sun Baked]

we'll just have to wait untill a dual 2.5GH owner pops the lid and looks on his g5 dies to see what speed they are marked at i did this with my mates dual 1.4GHz g4 back when it was debated weather it was a 1.4GHz cpu or an overclocked 1.25GHz one, the die was marked ppc 7455 1400 in little gold writing over the purple die. proof that they were 1.4GHZ moto rated chips

Yes, but that was enough proof for everybody to say they were overclock -- even if only by 20MHz.

Apple improved the heatsinks, which allowed them to run a hotter chip.

Apple was also the only customer for a CPU in the high W power dissipation range from Motorola, and since they no longer used, them Motorola isn't supplying them nor testing for them.

The PowerMac G4 upgrade market is just too small a niche market for Freescale to make the effort.

 

[ddtlm]

MikeLaRiviere:

Yep yep yep. The 2MB P-M's are the 90nm ones. (Why did IBM only put 512k of L2 on the 970fx? Makes me sad.)

 

[Zaty]

They can't be overclocked

Apple can't sell machines using overclocked CPUs. Why? Overclocking may decrease the lifespan of a CPU. Apple would get into lot of troubles if many of those $3000+ machines died after say two years or so because of their CPUs running at clockspeeds above what they're were rated for by IBM.

 

[johnnyjibbs]

I don't think they are overclocked. Going from 2GHz to 2.5GHz is a hefty leap and, even on a smaller processes, would run hotter than the previous generation 130nm 2.0GHz chip. The gains for going to 90nm in terms of heat and power consumption are obviously less than IBM and Apple (and Intel for that matter) originally anticipated.

As there is no difference in performance between a 90nm and 130nm chip rated at the same speed then it makes sense to put the old 130nm 1.8 and 2.0 chips in the lower and mid-end G5s, plus maybe 90nm chips that are not stable at 2.5GHz (although these would fit nicely into Xserves and upcoming iMacs).

As someone else pointed out, this must be the reason why they stuck with 1.8 and 2.0 G5 machines and not introduce a 2.2 or similar spec. It also ties in nicely with the iMac situation, which is obviously going to go G5 in September and was obviously originally intended to be released at WWDC or around this time.

Oh, and as someone else also pointed out, quietness is also key. The liquid cooling replaces the alternative - a massive and very noisey fan.