• Order of the Butterfly
    Order of the Butterfly
    Posts: 278 from 2019/5/9
    From: Central Bohemi...
    I continue with interesting discussion started ( a liitle offtopic ) here: iMac G5 overclocking

    Little terminology corner:
    CPU bus: = Processor Interconnect ( IBM terminology ) = Elastic Interface ( Apple schematics terminology ) = Processor interface bus ( Apple bussiness terminology )
    Northbridge: = U4 ( Apple bussiness ) = CP945 ( IBM ) = Kodiak ( Apple schematics )

    Fortunatelly, I receive iMac iSight G5 ( A1145 ) and iMac G5 A1058 (which is very probably version overclocked in above links ) schematics.

    I can confirm, that resistors responsible for CPU bus clock configuration 3:1 -> 2:1 are:
    iMac G5 1.8 GHz A1058: R3012 -> R3028, exactly like mentioned in above links
    iMac G5 iSight 2.1 GHz A1145: R4712 -> R4728

    Accordind to Northbridge and CPU manuals, the CPU bus clock domain is independent from other clock domains, so CPU speed not change with change of CPU bus speed ( in opposite of G3+G4 overclocking, where CPU frequency derives from bus frequency).

    So, all this is theory. In praxis there still can remain risk of damage, because of:
    - inappropriate version of real iMac iSight and schematics (not too big risk)
    - Northbridge in iMac can have lower "Speed Classification", i.e. maybe in real is not 1.05 GHz capable
    - insufficient cooling after bus overclocking
    - damage during mounting / dismounting / soldering
    - other things I didn't notice

    [ Edited by sailor 20.05.2022 - 08:20 ]
    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
  • »19.05.22 - 09:28