PCI Bandwidth

Discussion in 'Macintosh Computers' started by bcharm, Mar 23, 2004.

  1. bcharm macrumors member

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    #1
    I'm putting together a file server with two Western Digital Raptor hard drives (RAID 0) and a FirmTek SeriTek/1S2 controller.

    Anyone know if the PCI bandwidth of the Power Mac G4 400 and 1.25 are the same? I believe the 1.25 is 64bit/66Mhz = 533MB/s. If the 400 isn't the same and has a bandwidth of 133MB/s could I still use it to serve 3-4 graphic design workstations (3 Mac, 1 PC) on a 100 BT switch?
     
  2. pncc macrumors regular

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    Jul 23, 2002
    #2
    You don't specify which G4 400 you have, but this KB article suggests the G4 400 w/ AGP graphics has 66MHz PCI slot
    http://docs.info.apple.com/article.html?artnum=58434

    You can certainly obtain access from multiple CPUs, the question is how fast will the access be? What OS are you running? Server?

    A 100BT switch can only push 10(ten) MBytes/sec out of the server right? Why are you worried about being only able to push 133MB/s??
    Regardless of the PCI bandwidth, your network is the bottleneck. Consider Gbit networking or FireWire networking.
     
  3. tomf87 macrumors 65816

    tomf87

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    Sep 10, 2003
    #3
    pncc's right. Your network won't transfer fast enough to fill the PCI bus.

    Your calculations are a little off though, pncc. 100 Megabit / 8 bits per byte = 12.5 Megabytes per second.

    Even with 5 clients pushing full throttle, it will only hit 62.5 MB/sec, so it should be plenty fast enough. Extra CPU's won't help because they share the same PCI bus.
     
  4. bcharm thread starter macrumors member

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    #4
    You're right about our network being the bottleneck, but our current file server is about to croak. It's a really old PII with SCSI drives running Win2000. With a new server in place we can then request a new gigabit switch and gigabit network cards. My fault. I should have asked whether it would serve 3-4 workstations with gigabit nics on a gigabit switch. The Power Mac G4 400 is AGP and I'm planning on installing OS X Server.
     
  5. bcharm thread starter macrumors member

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    #5
  6. blue&whiteman macrumors 65816

    blue&whiteman

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    #6
    thats what 95% of all pci is. even the 1.6ghz G5 has 64bit 33mhz pci.

    only time I remember apple using 66mhz pci was as a graphics slot in the blue and white g3 and the yikes G4. also, the 66mhz slots are 32bit.

    66mhz pci is agp 1x
     
  7. bcharm thread starter macrumors member

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    #7
    Thanks. I don't know why I was under the impression that the 1.25 G4 PM had a 66MHz PCI. I never really paid attention to this stuff before given this task. I found this article, which made PCI bandwidth much clearer to me.

    So does anyone know if adding a 32bit 33MHz SATA controller card ties down the PCI bus to 133MB/s, or if it just takes up half of the 266MB/s bandwidth of the 64 bit 33MHz PCI bus?
     
  8. tomf87 macrumors 65816

    tomf87

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    #8
    You won't slow the bus down that way, because the speed is the same (33Mhz). It's just the card only has a 32-bit data path versus 64-bit. It is possible for the PCI bus to run two cards at different data paths, but not different speeds.

    If the bus were 64-bit/66Mhz/33Mhz, and you dropped a 33Mhz card in, the entire bus would slow down to 33Mhz because the bus cannot run at two different speeds.
     
  9. Sun Baked macrumors G5

    Sun Baked

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    May 19, 2002
    #10
    I was going to show some of the bus diagrams but the Yikes diagram isn't showing up (but the Yikes should be the same as a B&W G3 -- with a G4 hacked onto the FSB) ...

    And note that the KeyLargo never changed through the MDD G4s -- everything was changed via the PCI bus or UniNorth. (basically the PCI bus stalled when the gig ethernet came out).

    G4 AGP 2x Diagram

    [​IMG]

    G4 AGP 4xDiagram

    [​IMG]

    G4 AGP 4x Diagram (gig ethernet)

    [​IMG]
     
  10. blue&whiteman macrumors 65816

    blue&whiteman

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    #11
    the yikes board had no agp 2x slot. the yikes G4 (first G4 tower ever) is identical to a B&W G3 inside. they both had a 66mhz pci slot for graphics which is agp 1x.
     
  11. blue&whiteman macrumors 65816

    blue&whiteman

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    #12
    sunbaked did an edit to correct his error while I was making the above post :)
     
  12. Sun Baked macrumors G5

    Sun Baked

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    May 19, 2002
    #13
    I thought they used to list the Yikes, can't remember if it was also a Grackle machine or not (which is the only B&W G3 they have on the site).

    Most likely is since all the G3s and the Yikes suffered from PCI bus problems related to the use of the Motorola chips.

    [​IMG]
     
  13. bcharm thread starter macrumors member

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    #14
    Thanks guys

    Thanks for all the help and info guys. (Cool diagrams!) I see now that I was worrying about nothing. The bottle neck wasn't either computer's PCI bus, but the Serial ATA controller itself. Looking at our current network, RAID 1 will definitely be of more use. Down the road, hopefully not too far, when we upgrade to gigabit, I'll switch the drives to RAID 0 and use an external firewire hard drive for backup. Sound about right? The Raptors were overkill weren't they? =P Will they end up stalling or something?
     

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