Stardate 20020822.1255

(Captain's log): After being linked for the third day this week from the front page of Macintouch, my refer traffic from there has been quite amazing. It's also amazing how disgruntled and outraged some people have been about my use of the term "overclock".

Dylan writes:

Just to let you know .. I opened up one of the new dual 1ghz G4 systems today and removed the heat sink ..

The cpu is an MPC7455, and is a 1000mhz part, not an 800mhz part that's been overclocked as you asserted in your article. Even _if_ Apple were to be overclocking these machines, the 933 would be a better choice to overclock to 1000mhz .. and overclocking the 7455 from 1000 to 1250 (25% higher) without serious cooling modifications would likely be VERY unstable. I find it hard to believe that Apple has folks individually testing their entire stock of 7455/1000 CPU's to find those rare gems that would withstand such a brutal oc'ing.

Also, there are legal issues with selling 1000mhz parts as 1250mhz, and 800mhz parts at 1250mhz. Apple would surely face class action down the road if they were doing this. I haven't been able to inspect a dual 1250 up close, but I would wager heavily that they are MPC7455/1250 parts. Certainly I'd concede otherwise, as mot.com doesn't currently list a 1250 part, but incidentally, they only recently posted the info about the 7455 reaching 1ghz... so this may not be reliable.

Also, it's entirely possible that the 1.25 is, in fact, a 7470 chip. This is less likely, but still possible. Only time will tell at this point I think.

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.

My brother has worked as a consultant in the chip testing industry for the last fifteen years. The electronics of chip testers is really tough to design, because what it does is to permit the tester to electrically simulate a motherboard environment, with the ability to drive some pins on the CPU and to monitor others to capture their behavior for analysis. But if the hardware is complicated, the programming is fiendish. There are traps galore, where if you test wrong one good part of the CPU can mask a failure somewhere else, or where two failures can cancel. The planning which is involved in determining the sequence of tests and how they're constructed has to be seen to be believed.

But Moto has to do that anyway, because they have 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 speed, then that would make it worthwhile for Moto.

Still, this kind of thing has happened in the industry before, by design. There was a period about three years ago when Intel mother boards for the PIII were available in both 100 MHz and 133 MHz versions, and Intel routinely filtered PIII's this way. PIII's with a 7:1 clock multiplier, for instance, were first tested at 100 MHz and if they failed then they were rejected. But if they passed, Intel tested them again at 133 MHz. Those which passed the second test were labeled "933EB", those which ran at 100 MHz but not at 133 were labeled "700E" and sold for a lower price. They were exactly the same chip, but the "EB" on the part number said that Intel guaranteed that the chip would run reliably at 133 MHz. (In practice, they overtest a bit. The testing clocks at each speed are actually a little faster than rated.)

There's nothing at all wrong with this. It's completely legitimate; it's not at all dishonorable. There was no rule that said that customers were somehow being ripped off because the 933EB was the same silicon design as the 700E.

If that is what Moto and Apple are now doing, I don't think it's dishonorable for them, either. That's not the point I was trying to make.

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 mul