• Order of the Butterfly
    Order of the Butterfly
    sailor
    Posts: 273 from 2019/5/9
    From: Central Bohemi...
    @MoerBoer

    I am not sure that things here are so simple.

    Normally (and with G5 too) you set the CPU speed by known System Bus speed and proper PLL setting (i.e. multiplier)
    Then CPU speed = Bus speed x multiplier

    Note: G5 have a little different PLL tables nomenclature, instead of "multiplier" uses "Ratio". But it is generally the same number. Ratio 3:1 = multiplier x3.

    In case of iMac G5 (I assumed here 2.1 GHz, model is not mentioned in your link) we have 700 MHz Bus, and CPU 2.1 GHz, i.e. multiplier x3 (Ratio 3:1)

    If you want change Bus speed to 1.05 GHz, you have to: Change Bus speed to 1.05 GHz somehow and change multiplier to x2 (ratio to 2:1).
    I wonder if this should be done by change of two resistors. But who knows. ;-)

    Not to say, that from System bus speed are often derived other speeds (RAM) and Northbridge also have his own frequency limit.

    I never overclocked G5, because the overclocking scale is very rough.
    Is OK with G4 change multiplier from x9 to x10.5 with System bus 133 or 166 MHz, but the G5 case is x3 or x2, it is 50% difference in frequency! And Bus speed increase in your case from 700 MHz to 1.05 GHz is also 50% step up.

    In any case, if somebody want to try it, I recommend at first check iMac G5 Northbridge max frequency, probably change RAM stick to higher speed (but here is also RAM onboard and it can be showstop).
    And first of all proof from other sources what exactly are R3012 and R3028 rezistors and how the frequency logic works in iMac G5.





    [ Edited by sailor 25.04.2022 - 13:37 ]
    AmigaOS: Micro A1-C, AmigaOne XE, Pegasos II, Sam440ep, Sam440ep-flex, AmigaOneX1000
    MorphOS: Efika 5200b, Pegasos I, Pegasos II, Powerbook G4, Mac Mini, iMac G5, Powermac G5 Quad
  • »25.04.22 - 11:31
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