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Message: <blockquote data-quote="ArthurEGoodwin" data-source="post: 1603079" data-attributes="member: 332498">Hi everyone, this is my first post here.I have been trying to understand how the PCI slots in my Power Mac G4 MDD 2x 1.25Mhz work and it has been very frustrating. The official specs from apple say: 1)  the graphics card is in a x4 AGP 2.0 slot (max theoretical throughput of 1066MB/s), and2) the four pci slots are 64-bit, 33Mhz and all 4 slots share a second bus.I have not been able to find anywhere that specifies which version of pci the slots are. A number of sites say the early G4s have slots that are pci version 2.1, which implies that the later ones have pci version 2.2, but I am unable to confirm that anywhere. Can anyone here confirm that the G4 MDD has pci version 2.2 slots?I have also been trying to understand exactly how the throughput for the slots on the pci bus work. I THINK all the following are true statements (but am not sure and would really appreciate it if anyone here can confirm or deny any of this):a) All cards in the four pci slots (and thus all devices plugged into these cards) share the theoretical maximum 266 MB/s throughput. b) Each card/device utilizes the throughput separately, sequentially, through timing/interrupts. c) Mixing cards of different Mhz on a single bus, slows the entire bus to the Mhz of the slowest card.d) Mixing 64-bit and 32-bit cards on the same bus does NOT slow down speed.e) 32-bit cards on the bus can only access 133 of the 266 max theoretical throughput; so if only 32-bit cards are on the bus the theoretical maximum throughput is 133 (not 266).Thus you cannot have one 32-bit card using 133 and another 32-bit card using another 133 of throughput at the same time.f) If both 64-bit and 32-bit cards are on the bus, the 64-bit cards can access all 266 MB/s, but the 32-bit cards can still only access 133 MB/s. (Thus there is effectively two tiers of throughput, a bottom 133 accessible by any card, and a top 133 accessible only by the 64-bit cards).g) pci 64-bit, 66Mhz cards are mostly backwards compatible (functioning as 32-bit, 33Mhz cards when plugged into a 64-bit, 33Mhz slot), and less frequently backwards compatible where they function as 64-bit, 33Mhz cards when plugged into a 64-bit, 33Mhz slot.h) pci-X 64-bit, 66Mhz cards sometimes work the same way as described in g), but less often.I would sincerely appreciate any info helping to confirm, clarify, or deny any of the above.ThanksArthur Goodwin</blockquote>

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