[Matthew Attoe]

Hello,

I apologise in advance if this is a really dumb question with a slap-in-your-face simple answer.

I was just wondering, are the 2.7's overclocked 2.5's or are they "genuine" 2.7 processors.

I take it that the 2.5's in 2.5 machines can't be overclocked due to the 1.25 bus speed? Is this correct?

Like I say, just wonderin'

Thank you,

Matthew

[bowwowman]

More than likely is that the 2.5's were originally intended to be 2.7's, but werent stable at that speed and were binned down to the 2.5 section......

this is a common practice at cpu fabs, it helps to keep yields up and costs down, which is a good thing

[OreoCookie]

The G5's bus speed is an integer fraction of the processor speed. If the cpu is clocked at 2.7 GHz, the bus runs at half speed, 1.35 GHz and a 2.5 GHz cpu's bus runs at 1.25 GHz.

I'm not sure what you mean by `genuine' 2.7 GHz here. The cpus run at 2.7 GHz and Apple guarantees that they work. It is totally independent of what IBM is doing. Like gpu manufacturers, they offer what the client wants. If only very, very few cpus would exceed 2.5 GHz, it would not make financial sense for Apple to sell them.

The same happens in the server space by the way. The Power5+ runs at 1.9 GHz in current IBM machines, although Hitachi offers them at 2.1 GHz.

BTW, you can overclock your G5, if you wish, but you will void all warranty.

[svtcontour]

I think what he means is, if you rip the cpu out of a dual 2.7ghz machine, will it say 2.7Ghz or 2700Mhz right on the top of it or will it say 2.5ghz?

[mduell]

Yes, as far as I know Apple runs all their CPUs at the clockrate recommended/stamped by the manufacturer (IBM or Freescale).

The 2.7 is really an overclocked 1.6 that IBM wanted to dump on the market; why else would they be so hot?

[Todd Madson]

I believe this all stems from the rumor spread by hardmac.com that
the 2.5 machines were actually overclocked 2.3 processors (thus then
necessitating liquid cooling).

I believe our original poster here is extrapolating that rumor, that the
2.7s then must be overclocked due to the liquid cooling employed.

Given that IBM's Bladeserver JS20s run at 2.2 ghz and runs with
PPC 970 processors, you would then guesstimate the 2.3 machines
are also overclocked by a bit.

Regardless if these chips are overclocked or not, they run at the speed
they were sold at and should give you trouble free service.

I love my 2.5 DP, it's fast and reliable. I'm sure in most cases the
DP 2.7's will be similarly reliable.

Overclocking a G5 chip has two challenges: one being thermal and
the other is the fact that the bus speed is so locked into the CPU
speed so the two go hand in hand.

My guess - any performance increase by one or two hundred mhz
will be negligible compared to the lack of reliability achieved by
pushing those chips beyond their stated specs.

The sensor on the backside of the memory chip on my machine has
seen temperatures as high as 216 degrees fahrenheit - I can only
imagine what a 2.7 might reach and I don't want to be anywhere
near it if it experiences some kind of catastrophic thermal runaway.

[chefpastry]

Originally Posted by mduell

Yes, as far as I know Apple runs all their CPUs at the clockrate recommended/stamped by the manufacturer (IBM or Freescale).

The 2.7 is really an overclocked 1.6 that IBM wanted to dump on the market; why else would they be so hot?

The old PowerMac Firewire 800 dual 1.42GHz models used 1.40GHz CPUs. They were overclocked by 20MHz.

[Matthew Attoe]

Hello and thank you for all your replies.

I wasn't trying to amplify any rumours or anything. I was a bit bored a work today and my mind was just wandering a bit when I thought "I wonder if...". I certainly didn't have any dark motives

Thanks again for your time,

Matthew

[mduell]

Originally Posted by chefpastry

The old PowerMac Firewire 800 dual 1.42GHz models used 1.40GHz CPUs. They were overclocked by 20MHz.

How do you get 1.40Ghz on a 166.67Mhz FSB with a realitstic multiplier?
IIRC they used a multiplier of 8.5 for a clockspeed of 1416.67Mhz (which rounds to 1.42 Ghz).

[Eug Wanker]

Originally Posted by chefpastry

The old PowerMac Firewire 800 dual 1.42GHz models used 1.40GHz CPUs. They were overclocked by 20MHz.

Well, the chips officially supported the 167 MHz bus, and the chips use only integer or half-integer multipliers:

8.5 * 166.67 MHz = 1417 MHz.

ie. You have to go to 1417 GHz (or else underclock to 1333 MHz) to make use of the 167 bus (which the chip supports). To get a 1400 MHz you'd have to use a 133 MHz or a 100 MHz bus.

[westrock]

Maybe this is how you should have worded it....

If you take a 2.7Ghz CPU and put it into a 2.5Ghz system will the system now run at 2.7Ghz? Or is it like a Mini where the chip is "stable" at a desired frequency, but in fact because of the mobo settings any Mini can be 1.25 or a 1.42 or a 1.5Ghz....just some chips aren't stable enough to meet Apples requirements of higher clock speeds.

For example, if you bought 4 2.7Ghz G5 CPU's and put them into a Quad 2.5, would you get a Quad 2.7? Or would you have a "really stable" Quad 2.5 because the mobo determines the speed?

[Lateralus]

The 1.25GHz Mini used MPC7447A1250s
The 1.42GHz Mini used MPC7447A1420s

They left Freescale rated for the speeds Apple ended up shipping them at. Whether or not some 1.25GHz Minis can handle 1.5GHz has less to do with Apple's own determinations and more to do with whether or not the chip came from a better 'batch' when manufactured at Freescale.

And the Dual 1.42GHz G4 used MPC7455B1420s, rated for 1.42GHz speed by Motorola. No overclocking.

[westrock]

I understand. I work at Texas Instruments and we do this too. You have a wafer with 1000's of the exact same chips on them. Some test better than others and thus are bin'ed as better chips. They are still the same thing though, just the way its implemented later determines the speed. They are not "overclocked", if anything the highest speed is normal and the lower speeds are "de-tuned" versions.

So perhaps, some of us are not saying that a 2.7 is just overclocked and nothing special, but rather could we take a 2.5 up to 2.7 speeds or is the 2.7 a different design all togther?

We also don't know the specifications that determine the speed. It could be intensive calculations at 3 hours straight, while doing some other task at the same time. The chances of me ever recreating those tasks are slim to none and thus my Mini will never have any problems. But Apple doesn't want poeple coming back and complaining. Kinda like tires I guess, you can take most any passenger tire to 100+ MPH for a 30 seconds, its the expensive high rated ones that can stay at that speed for a rediculous state wide police chase.

[mduell]

Originally Posted by westrock

Maybe this is how you should have worded it....

If you take a 2.7Ghz CPU and put it into a 2.5Ghz system will the system now run at 2.7Ghz? Or is it like a Mini where the chip is "stable" at a desired frequency, but in fact because of the mobo settings any Mini can be 1.25 or a 1.42 or a 1.5Ghz....just some chips aren't stable enough to meet Apples requirements of higher clock speeds.

For example, if you bought 4 2.7Ghz G5 CPU's and put them into a Quad 2.5, would you get a Quad 2.7? Or would you have a "really stable" Quad 2.5 because the mobo determines the speed?

The chipset should detect that the chips are rated for 2.xGhz and run them at 2.xGhz. However you may run into problems where the older chipset doesn't support the higher FSB speed (or support them stably).

The quads only have two CPU sockets, not four, so you can't put four single core 2.7Ghz chips in.

[westrock]

Originally Posted by mduell

The quads only have two CPU sockets, not four, so you can't put four single core 2.7Ghz chips in.

haha, i'm an idiot. I knew that damn sure and well!