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Discussion in 'PowerPC Macs' started by PowerMacFan, Oct 15, 2012.
what is the max i can OC a 1GHz MDD FW800?
According to Everymac.com, that Mac uses PowerPC 7455B processor which is the same which is used in 1.42GHz dual machines, except that 1GHz model has half of the L3 cache. It seems that your processor is running 133MHz FSB, there is one resistor on the motherboard which you need to remove to use 167MHz and achieve 1.25GHz clockspeed, if the chip and L3 cache can handle it. I have done this once but I cannot now find you the link with instructions. If I remember correctly, if change the FSB it will also change the memory speed from DDR266 to DDR333 so if you have DDR266 sticks installed they might not work after the modifying.
EDIT: What I find funny is that 1GHz is the maximum that Freescale (was once part of Motorola) advertises is 1GHz so it seems like all 1.25GHz and 1.42Ghz used overclocked CPU's by default:
I've OC'ed 1.0 single to 1.5 GHz (without L3 active) and 167 MHz OC'ed bus.
Max with 167 MHz bus was 1.17 GHz, fully stable and with L3 working.
L3 chips on my daughtercard were rated max 300 MHz and didn't want go higher than that.
BTW, welcome back LeoTheLion
wat if i just plugged in a 1.42 cpu in with no modifing?
if i new where the mb resistor was i could rip it out.
if i rip out the resister will my cpu be faster?
Clock frequency is formed by having FSB and multiplier. In you case FSB is 133 and multiplier is 7,5 so 7,5 x 133 = ~1000. The FSB is set by the motherboard so if you plug in 1.42GHz processor it will not run full speed, multiplier is in this case adjusted from the G4 processor daughter card or whatever it is called.
In PC world with early Athlons/Durons it was a common modding to unlock the multiplier and then adjust it and FSB to achieve higher speeds.
I have performed overclocking twice on G4's, first I removed the resistor on Dual 867Mhz to achieve 1100Mhz. Second one was adjusting multiplier up one on 733Mhz Digital audio to achieve 867Mhz.
Both of these had no real noticeable performance advantage, on Digital Audio I was of course able to install Leopard without permorming any addiotional tricks