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Apple Desktops Discussion of Apple's desktop machines including Mac Pro, iMac, Power Mac, and mini

Power Mac - Overclocking Dual G4 MDD 867MHz - L3 cache info


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thewk

 
Member Since: Feb 21, 2009
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I have succesfully overclocked Dual G4 867mhz machine by changing the FSB from 133mhz to 166mhz, I removed the two resistors, R676 and R22. I have tested that the machine is stable in Xbench 1.3, Geekbench and in normal usage. G4 chips in my machine are RX933PC so they are rated for 933mhz and now working at 1080mhz.

But, I looked up the Samsung L3 cache chips on my processor card and as far as I know, they are rated for 250mhz (-HC25). L3 cache in MDD models with 1MB of it operate at 4:1 ratio, meaning that the cache in my machine is already operating out of spec, at 270mhz.

Is there any software which I can use to verify the L3 cache speed? Xbench displays incorrect speed, ~4Ghz. I wonder if there is a way to modify L3 cache ratio to 5:1 so I could possibly overclock even further, to 1.25 Ghz? Probably I could just try and see if it can take it, but I would like hear if anyone in here has ever done overclockin for their Dual MDD 867mhz machines and was it how succesful?
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chscag

 
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I can't answer your questions but the fellows in this forum possibly can. Drop in and post your inquiry there.

Regards.
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thewk

 
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Ok, I did post a topic there, let's see if there is possibility to squeeze even more out of this old machine. It was fairly cheap for me so it's not huge loss even if it fails

However, I think it is nearly impossible without changing the cache multiplier to 5:1, when I Googled about this many overclockers were unable to even do 133 -> 166 mod. I did not even investigate L3 cache speeds before I went on modifying the processor cad, just came across that thing later
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thewk

 
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Well, no one seems to know so I just went and tried to raise frequencies to 1.25Ghz. First the machine booted with the traditional chime but I was stuck in Open Firmware complaining about illegal instruction. Second try got me the default white background with the chime, no Apple logo however.

I reverted back to my previous setting and machine is working fine again. One thing I could try would be raising voltage... but that's probably bit too risky, this machine is not going to be rocket no matter how well I would be able to overclock it
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