quick network question

wim · Post by **wim** » Sun Sep 16, 2007 2:23 am

will a gigabit ethernet card perform as fast as an onboard LAN chip (integrated to the motherboard), or would the pci slot introduce some bottleneck?

Arvo · Post by **Arvo** » Sun Sep 16, 2007 2:43 am

Standard PCI throughput is 133MB/s, Gigabit theoretical throughput can be about 125MB/s - thereby no bottleneck. In practice GBE throughput is usually much less (30-100MB/s, rarely up to 114MB/s) and depends largely on cable quality and network chip; with good PCI card you may get better speeds than with cheap onboard solution.

floffe · Post by **floffe** » Sun Sep 16, 2007 2:59 am

You have to remember that PCI bandwidth is shared between all devices on the PCI bus too, so that could make it a bottleneck (like if you have a PCI sound card, TV tuner card or something else).

Post by **NeilBlanchard** » Sun Sep 16, 2007 3:03 am

Hello,

I could be mistaken, but the onboard LAN is connected using the PCI bus, too, I think. If so, then the point is moot.

Traciatim · Post by **Traciatim** » Sun Sep 16, 2007 3:53 am

I could be mistaken, but the onboard LAN is connected using the PCI bus, too, I think. If so, then the point is moot.

http://www.anandtech.com/showdoc.aspx?i=2631&p=1

It really depends on the motherboard and mostly chipset. In this example from 2005 it shows the Intel Pro/1000 as an extension of the PCI Express ports.

nick705 · Post by **nick705** » Sun Sep 16, 2007 4:03 am

NeilBlanchard wrote:Hello,

I could be mistaken, but the onboard LAN is connected using the PCI bus, too, I think. If so, then the point is moot.

It varies from one mobo to another - most current boards have at least one PCIe LAN controller, so there's no practical bandwidth issues, but Abit IP-35 Pro for instance uses two regular PCI controllers (there's only six PCIe lanes on the ICH9R southbridge, and Abit wanted four permanently reserved for a second graphics card, as well as one each for the x1 slot and the JMicron IDE controller).

It doesn't normally matter in practice, as even a PCI GigE controller will be faster than a single HDD anyway, but if you have other high-bandwidth peripherals sharing the PCI bus (eg an HDTV tuner card) I guess you could conceivably max out the available bandwidth.

wim · Post by **wim** » Mon Sep 17, 2007 11:53 pm

ok, sounds as though it's highly unlikely to be any problem

thanks all

wim · Post by **wim** » Wed Jan 23, 2008 4:40 pm

sorry to dig this up again but i'm just about to order another card and it was going to be this
http://www.scorptec.com.au/product/9650/
and then i saw this
http://www.scorptec.com.au/product/21130/
is there really any justifiable reason to pay 380% more for pci-e architecture? when it say

The PCI Express Network Adapter from D-Link offers increased bandwidth, reliability, and more functionality than standard PCI network cards. It is specifically designed to allow throughput at rates up to 2Gbps, thus eliminating the bottleneck that exists with current 32 and 64 bit PCI bus architectures.

is this just marketing BS ?

jessekopelman · Post by **jessekopelman** » Wed Jan 23, 2008 8:48 pm

I think the real question is whether you have an application that uses 2 Gbps? It would take a pretty hefty RAID array to produce that much of a data stream. Meanwhile, what about the rest of your LAN? Can it support such speeds. Most consumer grade GigE switches (especially those embedded in cheap routers) can't hit full 1 Gbps unidirectional speeds. So, the PCIe card may well be more capable, but do you have a way of taking advantage of that capability?

aaa · Post by **aaa** » Wed Jan 23, 2008 9:47 pm

I got a used PCIe gigabit for $30...
Main reason was because I wanted to use the PCIe slot for something, as I only have a couple PCI slots that I want to save for other things.

Really, the "bottleneck" is only a problem if you have more than one high-bandwidth thing running at once on PCI.

(BTW, the marketing is talking about the PCIe 1x speed, which is 2.5gbps. Of course the card doesn't actually do that.)

Beyonder · Post by **Beyonder** » Wed Jan 23, 2008 11:02 pm

wim wrote: is there really any justifiable reason to pay 380% more for pci-e architecture? ...
is this just marketing BS ?

It may not be marketing BS; I think the PCI bus can be a bottleneck.

That said, you've covered the real argument: you'd have to be incredibly stupid to spend $120 for a gigabit network card, even if it was PCIe. I just don't think you're going to see any noticeable benefit over the cheaper card that justifies the price difference.

(if you really, really need a faster network, I'd spend the money on a quality gigabit switch that supports jumbo frames, and make sure your network is tuned well)