PCI question : 66Mhz vs 33Mhz and 64-bit slots

[Xuttah]

I'm building a server, and would like to eventually put a RAID controller in it. The controller I've been looking at is a 32-bit, 66Mhz card (so the datasheet says). I've never been concerned with anything other than 32-bit, 33Mhz PCI slots. This started my questions about PCI below.

1. What are the differences (mb requirements) between a PCI slot running at 66Mhz and one running at 33Mhz?
2. Can a 66Mhz slot run 33Mhz cards?
2a. If #2 is "yes", does that apply to both 32-bit and 64-bit slots?
3. Can a 64-bit slot run 32-bit cards?

Thank you!

 

[mechBgon]

I think you might be confusing the speed of the RAID card's onboard processor with the speed at which the PCI busses run. As far as I know, the only 32-bit PCI bus out there is the standard 33MHz one. What RAID card are you considering?

 

[Viper96720]

PCI has
32bit 33Mhz-133Mhz bandwith
32bit 66Mhz-266Mhz bandwith
64bit 33Mhz-266Mhz bandwith
64bit 66Mhz-532Mhz bandwith
2. Yes a 33Mhz card can run in the 66Mhz slot but both slots will have to run at 33Mhz. Same with 64bit and 32bit
3. Yes most can has to be 3.3V

 

[mechBgon]

Does a 32-bit 66MHz PCI bus exist (in practice, I mean)? I haven't ever seen one, but there's always a first time

 

[Pariah]

1. What are the differences (mb requirements) between a PCI slot running at 66Mhz and one running at 33Mhz?

Not trying to be a smartass, but 66MHz PCI slots are required for a motherboard to run the PCI slots at 66MHz. You will only find them on SMP boards currently or the rare single CPU Xeon boards.

2. Can a 66Mhz slot run 33Mhz cards?

Technically, yes, but very few 32bit 33MHz cards will work in 66MHz slots and if they do the other slots drop down to 33MHz.

2a. If #2 is "yes", does that apply to both 32-bit and 64-bit slots?

Don't really get what you are asking here.

3. Can a 64-bit slot run 32-bit cards?

Yes, you can run 32 bit cards in 64 bit slots and the rest of the slots will not drop down the 32bit.

As far as I know, the only 32-bit PCI bus out there is the standard 33MHz one.

32bit 66MHz cards do exist, though you will rarely see a 32bit 66MHz slot since the cards will work fine 64bit 66MHz slots without affecting the performance of the other slots. A few of 3Ware's RAID cards are 32bit 66MHz as are some of Promise's ATA and ATA RAID controllers.

 

[Pariah]

Originally posted by: Viper96720
PCI has
32bit 33Mhz-133Mhz bandwith
32bit 66Mhz-266Mhz bandwith
64bit 33Mhz-266Mhz bandwith
64bit 66Mhz-532Mhz bandwith
2. Yes a 33Mhz card can run in the 66Mhz slot but both slots will have to run at 33Mhz. Same with 64bit and 32bit
3. Yes most can has to be 3.3V

What do those second MHz ratings mean? There is no PCI slot that runs over 133MHz.

PCI-X
64bit 66MHz : 512MB/s
64bit 100MHz : 768MB/s
64bit 133MHz : 1024MB/s (1GB/s)


PCI:
32bit 33MHz : 133MB/s
32bit 66MHz : 256MB/s
64bit 33MHz : 256MB/s
64bit 66MHz : 512MB/s

 

[Xuttah]

The card I'm looking at is a Promise SX4000. It'll run on a 32-bit 33Mhz slot, but a few reviews I've seen say the performance is MUCH better running in a 66Mhz slot.

Only motherboards I can find with 66Mhz slots are SMP boards, which are running 64 bit, 66Mhz slots. Seems like the only boards capable of running PCI at 32-bit, 66Mhz are the ones the sites used for testing. However, I just priced out a Dell PowerEdge server for $449, which has 4 64-bit, 33Mhz slots, and a 3ware card fits those specs nicely.

 

[K6]

AMD 760MPX based mainboard are perfect for mixed 32/64 PCI.

the 64 bit PCI connect the NB and the SB of the chipset and gereraly there are 2 PCI 64 slots.

From the SB start a different PCI bus for 32bit card

http://www.msi.com.tw/images/product_img/mbd_img/6501.jpg
long PCI are 64 bit 66Mhz PCI

 

[Viper96720]

Isn't a 64bit pci slot still a pci slot? So you got pci that has more than 133Mhz of bandwith.