Overclocking...

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Overclocking...

Hi,

I just got a hold of an old Power Macintosh G3. Here are the specs:

Power Mac G3 Minitower
366 MHz PPC w/ 1 MB backside cache
320 MB RAM(will be moving up to 512MB-640MB)
6 MB VRAM
20 gig hard drive
24X CD-ROM drive
Floppy drive
Internal Zip 100 drive (SCSI)
ROM Version $77D.45F1 (rev 3)
Raytheon voltage regulator
Whisper personality card
Firewire/USB card
Operating System 9.2.2-OS X10.2.6

This is what I know about the computer from the person I purchased it from. He says the following.

The G3 processor in this unit is rated at 350 MHz for use in the Blue & White model. In a beige G3 with a stock 66 MHz system bus speed, you must choose to clock the chip at 333 or 366 MHz. The 350 MHz speed isn't available without messing with the system bus speed (far more risky than just overclocking the main processor). This machine seems quite stable at 366 MHz.

I'm not expert here and am aware of the possible side effects to overclocking but want to take the risk. I've tried overclocking the processor to 400Mhz and haven't been able to. I followed the jumper settings from a few different websites and I have had luck with the 300Mhz/66Mhz Bus setting and 375Mhz/83Mhz Bus setting. 333Mhz setting also works. The 400Mhz setting doesn't work.

Can I overclock the 350Mhz rated chip to 400Mhz? If so, do I need a fan? Without a fan will it damage the processor? Which bus speed should I use and what is the difference between the 66, 75, and 83Mhz bus speed? Is anyone willing to share their experience with this overclocking stuff?

Thank you,

Spencer

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If it just plain wont boot, c

If it just plain wont boot, chances are it would need a voltage tweak, as heat isnt an issue at boot up. As for the bus speed, in every case I have seen, 83MHz bus is perfectly fine for them so long as the CPU is in its range (as well as being the fastest). If your really thirsting after more speed, grab a 900MHz G3 upgrade, or for a cheaper route, look on ebay for a 400-500MHz G3 from apple or upgrade for zif sockets.

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How do I do a voltage tweak?

How do I do a voltage tweak? The highest I'm able to go is 375Mhz/83Mhz Bus. Do I need a fan running at this rate? I did get 375Mhz/75Mzh speed to work too, it seemed slightly faster than the 83Mhz Bus speed. Is this correct? I set all the jumpers right for the 400Mhz/66Mhz Bus speed on P3, P4, P5,and P7 and all I get is the startup sound and then a blank screen the rest of the time. If I did get the 400Mhz/66Mzh speed to work, would I need a fan? I'm happy with where everything is at now, would just like to see what 400Mhz would be like.

Thanks,

spencer

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IIRC, the 75Mhz bus will seem

IIRC, the 75Mhz bus will seem a little faster in some circumstances because it overclocks the PCI bus to 35Mhz (vs. 33), but slower in others due to the lower SDRAM clock--both differences are very small, however.

As far as needing a fan, that's a totally subjective thing. Touch the hotsink with your finger--does it need a fan? Does it need a better hotsink? Thermal Compound? Does the bus controller need a hotsink?

The answer to these questions can be found by experimentation. Does the computer overheat and crash? Do you want to overclock it even further? If both answers are no, then you've probably got enough cooling. Acute

As far as heat-damaging your CPU... If a setting runs the heat up too high, it'll probably crash the computer. If the computer crashes, you'll probably shut it off, right? When you shut it off, it starts cooling down. Chances of destroying your CPU from excessive heat are very low as long as you're paying attention to your computer.

Tyler

(Written on a G3/300 DT running at 400/78.8 with a big socket 8 hotsink, Arctic Silver thermal compound, and a fan. Planning on soon using a 450Mhz G4 ZIF, ThermalTake Volcano 6 Cu+ (giant PC heatsink), and shooting for 600Mhz)

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If it wont boot at all its no

If it wont boot at all its not a cooling issue. If it boots then locks up, it may be. (its very hard to kill a cpu by overheating it btw, as they almost always auto shutdown when they reach their thermal limit)

As far as voltage tweaks, this is not for the beginner. Very easy to smoke the CPU if done wrong.

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Great explanation! Thanks. :)

Great explanation! Thanks. Smile

I gave up on the 400Mhz setting, I think maybe I need a fan for that one. As far as the voltage tweak, I won't even try. I've settled for the 375Mhz/75Mhz bus and all seems very smooth here, even slightly smoother and quicker than 375Mhz/83 bus. System has been stable and I haven't experienced any crashes, data corruption, or video problems. I'll continue you to keep track for any strange behavior. For now I'm happy.

Thanks,

spencer

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Pushing the envelope.

I think that you are at the limit for the ZIF. Further boosts are "fun" only for the brave.
But why run at the bleeding edge if you have to worry about data corruption? It will only bite you in the ass later. I have ran many ZIFs in machines boosting the bus speed to the max, only to find, months later that I had to start over due to a corrupted OS, and files.

Why bother, the speed increases are only "on paper" you most likely won't notice any real difference in your use of the machine. Dont use benchmarks stats to compare speed. Small speed increases are not apparent in normal usasge at ALL!

Be safe, and enjoy.

Cheers.

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Hello, You've made some ex

Hello,

You've made some excellent points here. Thanks. Today I noticed my monitor begin to shake slightly back and forth which makes it irritating while reading text on the screen. So, I have gone back to my original setting of 366Mhz/66Mhz Bus speed just to play it safe. I'm happy with this setting too and you are right, the difference in speed is not worth it. I'll wait for a new G5 for more speed. I still have the monitor problem, not as bad though. I wonder if my monitor is going bad? I'll watch it. If not the monitor, I may do fresh install and see what happens.

Thanks,

spencer

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A reinstall isnt needed for w

A reinstall isnt needed for what your seeing. only three things it can be. video drivers (easily replaced), video card (pci add in), monitor is bad.

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crt display shakes

frequently caused by a nearby transformer eg: flourescent lighting, try moving the display somewhere else (another room if possible) and see if it still shakes.

If the bus speed can be set to 83mHz, why not use that? The main reason to NOT use 83 is if you have only 66mHz ram, but that's not an issue if you have PC100 or better. Also, 375 on a 350 is a very mild overclock.

dan k

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Monitor shake has disappeared

Monitor shake has disappeared. I moved entire system to the back room and that seemed to do the trick. Just haven't found the exact cause of the shakes. Could have been the overhead lights, not sure. Anyhow, I won't be doing a fresh install (wasn't looking forward to doing that). The higher settings weren't giving me any trouble to begin with and seemed to work fine with the higher bus settings (ram is PC-100), until today. I was overly worried that the system might be overheating I guess. Well, I'll continue to play around with the other settings again. Thanks again for the input.

spencer Dirol

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I wouldn't worry much about t

I wouldn't worry much about the system overheating.

I have a b/w g3 350mhz in my beige and I overclocked it a year about to 450mhz/75mhz bus speed (wish i could go to 83 but it won't boot even at 350mhz multipler) and it runs rock stable on jagauar. I leave the system on 24/7 and it has never glitched out because of thje overclcoking.

However I also have high quality ram in my system, (3 pc133 crucial sticks of 256 megs), and a huge custom machined pentium 4 heatsink and fan on my system.

Overclocking isn't the scary taboo mystery science that a lot of people make it out to be. If it crashes, its just to high, back down and try again.

I have never heard of someone actually killing a cpu via overclocking before.

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However I also have hi

However I also have high quality ram in my system, (3 pc133 crucial sticks of 256 megs), and a huge custom machined pentium 4 heatsink and fan on my system.

I didn't realize pc133 memory sticks would work on this machine. How much of a difference in speed between pc100 and pc133? Since I'll be upgrading the memory in the next few weeks, I'd consider purchasing pc133 if it's a considerable amount.

Thanks,

spencer

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No speed difference

There is no speed difference between pc100 and pc133 if the bus speed is kept at or under 100 mhz. THe only reason why i use the pc133 is that its all i had and that its high quality ram. Its overkill when i'm running a 75mhz bus speed.

If you had pc66 memory in there and tried overclocking to 75 or 83 mhz, it might fail because of underclocked ram. Thats why you use pc100/133 ram when you overclock a beige (its like insurance that the ram isn't the cause of overclocking flukes). But there is no gain to be gotten if you move up from 100 to 133mhz on a beige.

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P4 heatsink

How did you attach that big old peice of metal to the zif? Did you modify your mtherboard to anchor it?

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Understood, I'm off

Understood, Thanks.
Well, I'm off to order more memory this week and be happy. Smile

spencer

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ram config matters . . .

some 133 ram will work in a Gossamer, some won't. It's all down the ram chip types and DIMM configuration. I'd give you the skinny, but I can't remember the details and am too lazy to look it up.

If the ram doesn't conform to the spec Gossamer understands, the most likely fault you'll find is it will be only half seen by the Mac. That is, the Mac will see the incorrect 256MB DIMM as a 128.

The best course is to buy from a vendor who specifies their ram as suitable for your Mac.

dan k

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Oh yeah!!! Good point!! I

Oh yeah!!!

Good point!! I forgot all about that. The big thing is make sure that you get doublesided ram sticks if you go to 256 meg sticks. I'm not sure what a gossamer is, but the beiges (and I think the b/w) will only see half of a 256 meg stick if its not a doublesided chip. LIke if it only has 8 chips on one side and the other side is empty.

Jon
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IRC it may also have to do wi

IRC it may also have to do with the density of the chips, ie. a 256 stick w/ 4 chips per side is likely one with 32 megabit chips, and I think the older controller in the Beige can only use 16 megabit chips. So, when you get your RAM you want, say, 256MB, double sided, and 8 chips per side. 8x2x16 == 256. If you get a 4 chips per side stick, newer machines see 4x2x32 == 256 but the Beige can only see 16 megabits of the 32 megabit chips so then you get stuck with 4x2x16 == 128. This is also why 512MB sticks won't work. They use 32 megabit chips, at 8 per side. Newer machines see: 8x2x32 == 512, while the Beige would only see: 8x2x16 == 256.

Someone correct me if I'm wrong... Wink

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