[CentOS] 1U firewall hardware

Mon May 16 15:16:44 UTC 2011
Blake Hudson <blake at ispn.net>

> pci is a shared bus with a max of 2 gigabits.  you'll see a gigabit but 
> never see two or more.
32bits * 33MHz = 1,056,000,000 bps. PCI is an arbitrated bus with one
talker at a time (half-duplex), so it's only capable of half the data
rate of a 1Gbps (full duplex) network.

In practice, I've yet to achieve more than ~ 400Mbps on a PCI based Gbit
NIC, even PCI-X based Intel NICs often fall short (~600Mbps) despite the
theoretical bandwidth of the bus. In my experience, PCI-e is the only
bus fast enough on consumer PC hardware to sustain Gbit data rates.

On paper, PCI-e 1x should support two 1 Gbit ports (four ports if using
PCI-e v2.0). However, the multiport Gbit NIC manufactures all seem to
have settled on PCI-e 4x, similar to how gfx card makers have settled on
16x whether or not the card can use or benefit from the additional