[Fragicula]

I consider overclocking my old rev. a iMac. I've seen this guide form www.bekkoame.ne.jp/~t-imai/imacde1.html and it says that you can overclock it up to 333. Is a 100 Mhz jump really possible? What's about colling it? At the moment the cpu runs with 62C/143F. I think thats ok, but overclocking means more heat or not? Or was overclocking everything apple did as they shipped the 333Mhz iMac?

Thanks for any answer,
Fragicula

[joe]

Originally posted by Fragicula:
<STRONG>I consider overclocking my old rev. a iMac. I've seen this guide form www.bekkoame.ne.jp/~t-imai/imacde1.html and it says that you can overclock it up to 333. Is a 100 Mhz jump really possible? What's about colling it? At the moment the cpu runs with 62C/143F. I think thats ok, but overclocking means more heat or not? Or was overclocking everything apple did as they shipped the 333Mhz iMac?</STRONG>

No, Apple does not overclock their processors. No, Tak's Mystic page does not say you can clock a 233Mhz G3 by 100Mhz. All he did was decode the PLL jumper settings for the different clock speeds. To understand what's going on here you have to realize Apple does not make an entire new PCB every time they update the iMac. Instead, Apple saves money the same way the other computer manufacturers do - by manufacturing a circuit board that can support a range of processor speeds. That way, when Apple decides to release a faster model, they don't necessarily have to redesign everything from scratch. Instead, all Apple has to do is set the jumpers to match the new faster processor speed. But one side effect of this design is that it's relatively easy to overclock compared to the 'bad old days' when you had to buy clock crystals at various speeds to clock it up.

I'd say a more realistic overclock speed for an original aluminum 233Mhz G3 would be 266Mhz. That's assuming your particular G3 has enough overhead AND you could provide additional cooling to keep it stable. 300Mhz might be possible with extreme modifications (Peltier cooler, water block). But it's just not worth it at that point because it would be cheaper to get an accelerator with a faster rated chip. At least 1st gen iMacs (revA-D) can get an accelerator (processor upgrade card) - later models can't. But there are other bottlenecks in the 1st gen design (bus, graphics, IDE controller) that can slow things down even with a faster processor. Before you decide on a course of action, be sure you're taking everything into account. Either way, good luck. Regards.......joe

[Fragicula]

Thanks for your answer. I've now read the reports at xlr8yourmac and it sounds like it's possible to speed it up to 300, at 333 most of them didn't boot anymore. But at 300 some said they could do it without extra cooling. I really doubt in that because one of them said his system would run at 138 degrees CELSIUS. I can't imagine that this is stable. And because I have no idea how to get extra coolers into the iMac or on the processor I think that would be a bad idea.

But is it even woth to open the case to overclock it 33MHz? Would there be any difference at all?

Fragicula

[Carl Norum]

Originally posted by Fragicula:
<STRONG>I consider overclocking my old rev. a iMac. I've seen this guide form www.bekkoame.ne.jp/~t-imai/imacde1.html and it says that you can overclock it up to 333. Is a 100 Mhz jump really possible? What's about colling it? At the moment the cpu runs with 62C/143F. I think thats ok, but overclocking means more heat or not? Or was overclocking everything apple did as they shipped the 333Mhz iMac?</STRONG>

Well, the answer to this requires a quick explanation of how processors are built. At the semiconductor manufacturing plant, all of the chips are built at the same time - in the case of the first few sets of G3's, that would be the 233,266, etc. The 233 and 266 are made at the same time, on the same piece of silicon, with the same masks. Everything is identical. The speed difference comes from the final chips themselves. Each one is individually tested, and then gets thrown in the 233 bin or the 266 bin depending on its test results (minor flaws in the manufacturing process can cause speed differences).

So the answer is that while your chip may be built using the same technology as a G3-333, it would be quite a stretch to overclock it that far. Especially if you're running at 62 C right now. I would try for 266 or maybe 300 with your particular chip.

Also remember that the "sweet spot" for overclocking is about a 5x bus multiplier. Since your machine has a 66 MHz bus, going higher than 333 would be a waste.

Just go ahead and try the OC job. If the machine doesn't work afterwards (or works badly), you can just put it back the way it was.

[x user]

Basically if you have to ask that question. Overclocking is not for you. It takes a bit of background in electronics. Knowledge of what yo look for if you overclock is too much. And most of all a cool head, and ability to solder resistors the size of ants.

Edit:
Just realised some ants are big. The size of SMALL BLACK ANTS

[ 02-24-2002: Message edited by: x user ]

[Fragicula]

Doesn't sound good for my iMac to get speeded up
Would special tools be requiered to move the resistors? If not maybe I'll try a 266 overclock. If I could place a fan directly over the processor, I'd do a 300. But on this mainboard I wouldn't know where to plug it in even if I had the space.
Regarding this, PC mainoards are much simpler.

Fragicula

Edit:
Wait, solder the resistors? You can't plug them into the other position?

[ 02-24-2002: Message edited by: Fragicula ]

[x user]

You have to unsolder them, then solder then in new places.

[Fragicula]

Ok, this project died before it began

Thanks for the warning

Fragicula

[cdhostage]

Yeah, I dissassembled my Rev D iMac to try and overclock it. Man, those little resistors are small. Tiny, even. Sorta about half the size of a pinhead.

Well I'm typing this on an OC'd Ti 500-&gt;550.

[seanyepez]

Overclocking an iMac is stupid. Replacement parts are available at sky-high prices, and the performance gain isn't noticible for most things an iMac does.

The original iMac didn't have a very good cooling setup. The second-generation iMacs are even harder; they lack any sort of active cooling. The current iteration is even harder to overclock; the G4 produces a lot of heat already.

My Athlon is overclocked to 1,667 megahertz from 1,533 megahertz. This is a safe overclock because I have a copper heatsink and run the processor at 112 degrees Fahrenheit. A processor running at 143 degrees Fahrenheit will end up burning. It's just not safe.

[Jansar]

The iMac is just not made to be messed with. Everything is assembled differently. Even the 3D card is stuck on the motherboard.

[Fragicula]

Well, a processor runnung with 143 F won't end up burning. If GaugePro doesn't give just imaginary numbers, my not overclocked iMac runs with that when I convert mp3's. But it's hot;-)

Fragicucla

[Davidarm]

I overclocked my wife's Rev B iBook from 300 to 400 mhz, and it's been solid as a rock for two months now...runs 15-20 degrees hotter sometimes, but between the OC and the new IBM fluid bearing 20G HD, it's like a new machine...very noticeably faster...

[Big Mac]

Originally posted by Davidarm:
<STRONG>I overclocked my wife's Rev B iBook from 300 to 400 mhz, and it's been solid as a rock for two months now...runs 15-20 degrees hotter sometimes, but between the OC and the new IBM fluid bearing 20G HD, it's like a new machine...very noticeably faster...</STRONG>

Wow, that's a major accomplishment and a major chore. I salute your technical prowess. I'm sure that procedure was not for the faint of heart.

[Carl Norum]

Originally posted by Fragicula:
<STRONG>Well, a processor runnung with 143 F won't end up burning. If GaugePro doesn't give just imaginary numbers, my not overclocked iMac runs with that when I convert mp3's. But it's hot;-)</STRONG>

Gauge Pro does give imaginary numbers. The temperature register on a PowerPC chip is accurate only to +/- 12 degrees C (22 degrees F), at least according to the IBM web page.

[Fragicula]

+/- 12C wow. That makes the thing almost useless

Fragicula