This is totally untrue and is being spread by misinformed people. If you look at the actual CPUs, which is hard to do since they have a big honkin' heatsink on them, they have the actual Motorola part number which indicate they are either 1.42, 1.25, or 1 GHz CPUs. I think alot of people think they are overclocked because Motorola hasn't updated their PowerPC website in ages, or because of rumors that the PowerPC G4+ only ever made it to 1GHz or 1.25GHz or because of the heat issues of the current machines. Obviously Motorola has gotten decent yields of 1.25GHz and 1.42 GHz chips.
There's an interesting article by Steven Den Beste about whether or not the G4s are overclocked or not. He seems to think that they are, but not in the usual sense of the word.
I was using the term "overclocking" not in the pejorative hobbiest sense, but rather to mean that these are old parts, running faster. It may be that we have a disagreement on whether that is actually correctly designated "overclocking", but that's unimportant. Irrespective of what words we use to describe it, I still think that's going on, and that's because if Moto were still developing new G4's, then it seems as if they could have released ones which were not only rated for a higher clock but which also had a higher multiplier. I am extremely suspicious of the fact that the new 1.25 GHz Macs are still using a 7.5:1 clock multiplier, just as the old 1 GHz Macs did. Why isn't the multiplier higher?
It's a lot easier for Motorola to rate old 7.5:1 CPUs to run at a higher FSB than to actually design a new part entirely, if in fact they discovered that a lot of the old parts actually could run faster (which would not be particularly surprising). A higher rating on an old design only involves changing the testing and labeling.
My spidey-sense tells me that the reason Motorola is willing to test and certify old parts for a higher clock rate, and that Apple actually designed a new computer to use them, is because Motorola doesn't plan to bring out new chips which are substantially faster any time soon (or maybe ever) and Apple knows it. Pointing out that Moto is involved in certifying the new parts doesn't change that, because it still doesn't explain why it is that Apple was willing to put so much effort into these systems, if they knew that new CPUs, with higher multipliers, would be coming.</blockquote>
Another uninformed person that doesn't know what he's talking about and using a very weak excuse. Apple has PowerMacs at 1.25 and 1.42 GHz and Xserves at 1.33 GHz. All these use a 166.6Mhz bus. 7.5 x 166.6 = 1250MHz = 1.25GHz, 8 x 166.6 = 1330MHz = 1.33GHz, 8.5 x 166.6 = 1416MHz = ~1.42GHz. Apple is already using an 8.5 multiplie,r and besides, the 1.25GHz are using a 7.5 multiplier because Apple upped the bus speed. At some point you have to up the bus speed, you can't keep on increasing the multiplier. And besides, as far as I know Motorola (and other chip manufacturers) doesn't rate chips by multiplier, but by MHz. This is kind of evident by their part number scheme. Also a chip that is rated at 1.25 GHz could go in to a machine with a 100 MHz bus or a 166.6MHz bus with different multipliers and still run at 1.25GHz. It could also go into a machine with a 133.3MHz bus, but it would only run at 1.2GHz. I think he's just talking total BS.
I'm not sure if you read the entire article, but Den Beste stressed that Motorola, not Apple, is doing the overclocking:
<blockquote>I'm not at all surprised to learn that the new CPUs are labeled by Motorola at the speed Apple is selling them at. Apple doesn't have the technical ability to test the parts to see if they'll run faster.
Moto does, because Moto has to have that ability anyway. Every CPU which comes off the line has to go through a testing process which is extremely complicated and elaborate, performed by equipment of unbelievable sophistication. That testing process is intended to guarantee that all parts of the processor work as designed at the specified clock rate.
...[Motorola has] to confirm that every chip works before they can ship it. Their chip testers do so at (a little bit faster than) the rated clock speed of the part, but if the testers are capable of running a lot faster (which would be expected) then it wouldn't be too hard for Moto to test certain groups of chips twice, once at 133 MHz and if they pass that then again at (a bit faster than) 167 MHz. The main reason for resisting that is that it doubles the testing time, and testing already takes too long and costs too much. Testing is a potential bottleneck on most IC lines because the process is inherently slow and extremely capital intense. But if Apple was willing to pay a higher price for parts certified to run at a higher price, then that would make it worthwhile for Moto.
It's strange that Motorola has labelled these chips XC7455 rather than MPC7455, and are running these chips at a high core voltage.
It's also strange that Apple totally redesigned the PowerMac case in order to improve airflow and house the giant heatsink the XC7455 requires for proper operation. Heck, Apple had to move from aluminum to copper for the heatsink in the PowerMac G4 1.42GHz.
The explanation that seems most likely to me is Motorola is pushing the G4 above and beyond what it was originally designed to do in order to keep Apple happy. I think Apple is testing MPC parts at higher speeds and voltages, and those that pass the tests are labelled XC and shipped to Apple. Those that don't pass are labelled MPC and sold to other Motorola customers.
Of course, this is pure speculation on my part, but given the fact that PowerPC doesn't seem to be a priority for Motorola these days, and this is a quick and easy way to keep Apple happy, I don't think it's that far fetched.
 For what it's worth, Den Beste's article was written in August 2002, before the 1.42GHz PowerMacs and 1.33GHz XServes. I also think Den Beste is used to Intel and AMD chips with fixed multipliers, hence the fact he only discussed the 7.5:1 multiplier.
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