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PCI Bandwidth

B

bcharm

macrumors member
Original poster
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?
 
bcharm said:
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?
Click to expand...

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.
 
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.
 
pncc said:
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.
Click to expand...

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.
 
blue&whiteman said:
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
Click to expand...

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?
 
bcharm said:
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?
Click to expand...

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.
 
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

Sawtooth_L_01.gif


G4 AGP 4xDiagram

CW_L_01.gif


G4 AGP 4x Diagram (gig ethernet)

tan01.gif
 
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.
 
blue&whiteman said:
sunbaked did an edit to correct his error while I was making the above post 🙂
Click to expand...
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.

PowerMacG3-8.gif
 
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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