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PCI-X, 64 bit slot 32 bit OS

Paul Caldwell

New member
Similar question to my first thread.


What is the general opinion on this? If you have a board that has a PCI-X slot, true 64 bit card slot (not to be confused with PCI express) and you install XP on the board, will that particular card slot really get a 64 bit environment? Point here is with a scsi 320MB transfer, you can't get past 160mb transfer if you put the card in a normal 32bit PCI slot.

I don't mind getting a board with a 64 bit slot, but I need to know if I can get that slots 64 bit support with XP, or if I need to go to XP 64 bit OS.

Thanks
PFC
 
Paul you are mixing up issues. 64 bit PCI-X refers to the width of the data transfer bus and has no relationship to 64-bit CPUs. So long as you can get 64-bit drivers you should be okay.


That said, PCI-Express x4 and x8 RAID cards are something you might explore using too if you are buying a new motherboard.
 

Josh Liechty

New member
Sean DeMerchant said:
Paul you are mixing up issues. 64 bit PCI-X refers to the width of the data transfer bus and has no relationship to 64-bit CPUs. So long as you can get 64-bit drivers you should be okay...
This could be slightly confusing; PCI-X cards that use 64 bit transfers will still use 32 bit drivers under 32 bit XP. 64 bit drivers are required only for XP x64 or 2003 Server x64. As you correctly stated, the width of the data transfers is not related to the type of operating system used (32 bit or 64 bit).
 

Paul Caldwell

New member
That was my main issue, since XP professional is not a 64 OS, is there any point in using a true 64 bit slot, i.e. PCI-X in a XP Professional environment? Yes, XP will see it and work, but IMO you would still be only working at a 32 bit rate, i.e. 160mb.

To take advantage of the full speed of the PCI-X slot, 64 bit, I would need the XP 64bit version. or Server 2003 (a version of it that is 64 bit).

I am trying to get the maximum throughput out of my scsi bus, but didn't want to have to move up to XP 64 bit.

PFC
 
Paul2660 said:
That was my main issue, since XP professional is not a 64 OS, is there any point in using a true 64 bit slot, i.e. PCI-X in a XP Professional environment? Yes, XP will see it and work, but IMO you would still be only working at a 32 bit rate, i.e. 160mb.
The 64 bit PCI-X slot transfers data between the slot and the other components of the motherboard using a bus capable of transferring 64 bits in a single transfer. This capability is independent of the capabilities of the processor, i.e., the transfer is not required to pass through the processor, and is not dependent on the processor's capabilities.

A white paper on PCI-X comments as follows.

Full Software Backward Compatibility
To make the migration to PCI-X 2.0 easy, full software backward compatibility is also faithfully maintained. Operating systems that support current generations of PCI also support PCI-X 2.0: Window 3.0/95/98/2000/XP, Linux, OpenVMS, Novell, UNIX, OS/2, SCO, Nonstop Computing, etc. All the current addressing, registers, and protocols are accepted and interpreted correctly by PCI-X 2.0. Software compatibility is also true of the BIOS, and the device drivers. They don’t require any change; by default they are compatible with all speeds of PCI-X 2.0 adapter cards.​

To take advantage of the full speed of the PCI-X slot, 64 bit, I would need the XP 64bit version. or Server 2003 (a version of it that is 64 bit).

I am trying to get the maximum throughput out of my scsi bus, but didn't want to have to move up to XP 64 bit.

PFC
As noted above, no, you don't need to change operating systems to realize the full capability of a PCI-X SCSI card in a PCI-X slot.

Bob
 

Josh Liechty

New member
Bob Peterson's explanation is the best yet. I didn't say, but should have made clear that using 32 bit drivers in XP does not deprive a PCI-X peripheral of its ability to transfer data at full speed with 64 bit transfers. In short, you've no need to upgrade to an x64-optimized operating system unless you need it for some other reason.
 
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