• Welcome to Overclockers Forums! Join us to reply in threads, receive reduced ads, and to customize your site experience!

Mobos that support true PCI-E 4x?

Overclockers is supported by our readers. When you click a link to make a purchase, we may earn a commission. Learn More.

eduncan911

Member
Joined
Oct 27, 2004
Location
Upstate NY and NYC
Got a question, what mobos support true PCI-E 4x/8x throughput of the secondary slots? Talking non-SLI boards and Intel Chipsets (not NVidia).

Here's my concern: With the hype of PCI-E 16x for graphics, there are a number of mobos with additional 1x, 4x, and 8x slots. I can't find much information, but I'm worried that they are routed through the limited PCI 32bit controller bus. Limiting to 132MB/s. It would make sense for manufacturers to cut corners to do this.

My goal? High data throughput using the 4x PCI-E slot. I was dead set on a PCI-X 64bit setup, but Supermicro is about the only one that makes one with a decent PCI-E and 775x socket. And I haven't had much luck with Supermicro's customer support or products.

Here's the card I'm planning on at the moment:

Promise SuperTrak EX8350 PCI-E 8-port SATA RAID Controller for a RAID5 setup

Current plans are to start with five 500GB Baracude drives in RAID5. This will easily exceed the 132MB/s limit of PCI. Hence why I am looking into PCI-E 4x or 64bit. I like the idea behind PCI-E 4x.


Does anyone know if the Asus P5WD2 Premium board's 2ndPCI-E slot that supprots 4x is true 4x? Or just hype that is forced through the PCI's standard bus?


[off topic]
I'm getting close to putting togather my MCE machine that also will act as my file server. As you can see in the signature, I don't play when it comes to my personal machines. :D

The mobo is still up in the air, but current requires for it are:

- One PCI-E 16x slot (graphics)
- One PCI-E 4x or 8x slot (data)
- Two PCI 32bit slots (at the least, 3 preferred)

I prefer the Intel 955x chipset as I have a number of these chips around here. And I haven't had much luck with NVidia's chipsets. No, I don't care about SLI for my MCE machine. It won't be a highend gaming computer.

The current picking is the Asus P5WD2 Premium as I've used this and the P5AD2 before - at 4.2Ghz. I won't be overclocking much since I'll be running low-heat versions of the 775 chips with fanless HS and custom heat ducting for the airflow to be effective across the CPU's HS and mobo's HS. Drives will be in seperate enclosure.

Also since the release of the newer "True SLI" boards, I suspect the people with P5WD2's to get rid of theirs cheap soon. Hey, I just don't throw money at my computers. Yeah, I may spend a lot but I research for the best price and products first. ;) And there's good reason for me starting at 2 TB of storage.
[/off topic]
 
Last edited:

Snugglebear

Member
Joined
Aug 2, 2005
On modern Intel chipsets the 32/33 PCI interface is off a sperate line from the Southbridge (e.g. ICH7). In the case of the 945 and 955 chipsets, the ICH7 Southbridge has 6 total PCIe lanes plus other avenues for the sound, SATA, USB, and legacy (BIOS et al) peripherals. Manufacturers are free to use those 6 PCIe channels as they see fit, though they are seperate from the 32/33 PCI bus.

The amusing thing is that PCIe channels are more flexible than previous PCI busses, so board designers are free to do what they please with them. It is no more difficult to supply a 1x, 2x, or 4x PCIe slot at the end of the channel(s) than it is to use a PCIe 1x channel as a dedicated connector with a PCI-X chip. Just as easily an engineer can place an additional SATA, SCSI, or ethernet controller at the end of that PCIe line. Hell, if it wasn't for interrupt limitations you could probably have 7 seperate 32/33 PCI busses attached to an ICH7.

In the end, the point here is that chipset design is progressing towards the opposite of your expressed fear. With older chipsets and boards you do have to be wary of where peripheral controllers are attached, but these days, with the P2P nature of PCIe, the tide is turning. That's not to say everything is totally independent - I've seen a few boards share PCIe lanes with PCIe slots and GigE controllers or other nonsense - but it's getting there. If you need to check on a specific chipset, check Intel's docs and pay attention to the chipset diagrams. Many board manufacturers like Supermicro will also place chipset & board block diagrams in their manuals, so it pays to read them (e.g. the PDSG4 manual shows that SM uses 4x PCIe slots to link with a PCI-X controller in order to provide 2 PCI-X slots and a home for the onboard SCSI controller).

For the Asus you ask about I do not know how they build that 4x PCIe slot, but I can tell you it has to have at least a 1x PCIe lane running to it.
 

JCLW

Member
Joined
Apr 1, 2002
eduncan911 said:
Also since the release of the newer "True SLI" boards, I suspect the people with P5WD2's to get rid of theirs cheap soon.
The only board I'd take over a i955 board will be a i975 board ;)

eduncan911 said:
*bump* reviving thread
I think Snugglebear answered most of your questions. As he pointed out, you might find a parallel PCI bus running off one or more PCIe lanes, but you won't find any PCIe lanes running off the PCI bus.

The P5WD2 offers 2x or 4x electrical support on the 2nd 16x physical slot.

The Promise EX8350 has proven itself very slow in RAID 5 so far, to the point where running it on the PCI bus wouldn't make any difference. The Areca ARC-1220 is considerably faster.

Also, if this is just for file serving, remember that you're always going to be limited by your network link. If you're running 100mbit then that only gets you 10MB/s. If you're running 1gbit then you can get close to 100MB/s, but only if you start using jumbo frames. So PCIe 1x would be more then enough anyways.
 
OP
eduncan911

eduncan911

Member
Joined
Oct 27, 2004
Location
Upstate NY and NYC
JCLW said:
The Promise EX8350 has proven itself very slow in RAID 5 so far, to the point where running it on the PCI bus wouldn't make any difference. The Areca ARC-1220 is considerably faster.

Ok now, don't just spit out random information. ;)

Give details. Like where did you read that? What tests? What mobo were they using? Etc.

That's exactly the type of test results I am looking for (and articles).