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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), and
2) 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.
Thanks
Arthur Goodwin
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), and
2) 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.
Thanks
Arthur Goodwin
