i'm seriosly considering o/cing my iMac DV to 1GHz. do you think it's stable? what kind of cooling would i need? and how would i install/ power that cooling? also, does anyone know of an LCD screen they would perhaps GIVe me? or sell to me cheap? any input would be imensly helpful.



Current spec on the iMac are as follows:

processor: 400 MHz PowerPc G3
Screen: CRT
Graphix: ATY Rage 128
RAM: 640 Mb
Hard Drive: 160 Gb (iMac cut it to 130 ish)
i dremmeld a hole in the back and mounted a 12v fan inverted to suck heat out of the comp, pluss i left the clear vented handle off.

I'd suggest not going all the way to 1 GHz right off the bat. If you fry your processor, that will be the end of it. Maybe you should aim for something like 700 or 800 MHz, and then gradually step it up to make sure no issues arise. As far as cooling, an LCD replacement for the CRT will not only open it up, but speed up heat dissipation, so that is a definite start. With that extra space, you might be able to put a better heatsink over the processor, and perhaps add a fan. You might also consider putting a fan at the vent on the top drawing fresh air in. That will expedite the cooling process, and is how the G5 case cooling system works.

JediJoker is right, you must take overclocking slowly! Some procesors can handle jumps of several hundred mHz. An identical processor may not. Please be very careful and bump it up a little at a time, and def add cooling. Good Luck!

Post edited by: anil8tor, at: 2005/09/23 11:36

First, Im afraid the highest you will probably get is 500-550. It will need better cooling too. My suggestion is that you lap the heatsink and use arctic silver on it, the add an extra fan to the case. That will get you started.
-maestro

I would have to echo what everyone else has stated a gradual move would be the best, also the crt lcd replacement is a great idea it would free up tons of space and help to get a major heat generator out of the box. Look in the mod guide to see someone who found a lcd to fit almost perfectly in an iMac case.

Maestro is right: I can almost promise you that you will not make it to 1Ghz and retain stability--or even a working processor. Even with water cooling, you won't make it with that chip.

That doesn't mean you can't OC it though.

You would be lucky to get atleast 50 to 70MHz more out of that if you're lucky. The older iMacs have the CPU on the backside of the logicboard and basicly uses the frame of the case as the heatsink. Not bad but the heat onlt travels so far. Now if you can cut away the frame so you can fit a standard size (2 to 3 inch) tall heatsink it will add some extra cooling. Other then that if you plan to try majorly overclocking it I would use a diffrent case.

the link for the o/c guide is http://www.bekkoame.ne.jp/~t-imai/imacde1.html. it has the settings for it, so assume it's possible.

Theres settings for my B&W to go at 800Mhz but it can't go even close to 800MHz.

how fast do you think i can get it? and what holds it back?

Theres is no way of telling, You have to up the speed in small amounts and then check stability and heat factors, if its stable try the next higher speed. Its not an exact science when it comes to over clocking, more like vodoo
And as I said befor no two processors are the same, Yours may handle 200mHz over normal or it may only take 50mHz. Its all about stability AND heat, you must keep the processor cool to over clock. You are asking it to run beyond its rated capacity and this means it will generate more heat. Too much heat :evil: and you fry it.

Just try a small amount at a time and see what happens. Your mac will let you know if its unhappy. :S
-maestro

Ok IBM makes the PPC CPU right? Well heres a little lesson what Intel does with their CPUs. I think SUN and IBM does the same thing.

Intel basicly takes a CPU that was made for pushing 100MHz. They then take it and make it push 200MHz and lock it as the default clock. This is how the CPU runs very hot and needs a heatsink. Probly why the G5 has a big ass heatsink aswell. Basicly to save money from building a CPU some scratch they just take what the already have and modify it so it runs faster. All what overclocking does theses days is raiseing the FSB and the Multiplyer.

Heres how I see it. They pump the CPU with tons of caffine and when you overclock it you're making it drink even more caffine. If you go any higher it will go nuts and probly have a heartattack meaning the CPU will fry.

I remember reading a article that Intel's frist line of Pentiums were infact a customized 486 at 90MHz with a built-in 487 at 66MHz and more cashe built in. Then down the road it was overclocked to 166MHz then they made a new one from scratch and they built MMX.