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Power Macintosh G3/G4/G5

Yammayamma
User

Posts: 3

G4 PCI slots - 2008/08/29 02:51 A question about the 33MHz 32/64-bit PCI slots in Mirror Drive Door G4s:

I gather that the 4 slots share the same bus so that the cards in different slots are in contention.

If I put a 32-bit card in, will make the whole bus run at 32 bits, slowing down any existing 64-bit cards?

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Yammayamma
User

Posts: 3

Re:G4 PCI slots - 2008/10/08 02:00 I think I found the answer to my own question. Here it is:

The different cards each have to take their turn using the single PCI bus of the G4. When a 32-bit card is using the bus, it negotiates a 32-bit connection, when a 64-bit card has data to transfer, it negotiates a 64-bit wide connection.

The key here is when and how often the cards are going to need the bus, regardless of width. If one hogs the bus by needing to use it constantly it won't leave much room for other cards.

For example, adding both Gigabit ethernet and Serial ATA cards to a G4 server isn't such a good idea: When data needs to be served onto the network, both cards will be busy at the same time, then they will both be idle, waiting for the next data request.

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Scuzball
User

Posts: 84

Re:G4 PCI slots - 2008/10/09 20:30 So, will there be any problem having a SCSI card and a Firewire card in the same Quicksilver G4?
One is connected to an internal SCSI drive, the other to an audio interface.

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rich415
User

Posts: 47

Re:G4 PCI slots - 2008/10/19 23:11 sounds like a design flaw... like it kindof cripples the machine... i wonder if they just didnt think far enough into the future... lol

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