Originally posted by: fire400
the pci-e bus is capable of using terabit cards. the pci bus is capable of gigabit nic cards, I think you're better off with a 32-bit pci card..
TERABIT cards? I don't think so.
Remember that for each pcie lane an 8/10 encoding scheme is used so the actual rate is less than the raw gigabaud rate.
Now x4 PCIe is NOT sufficent to handle even 10 Gigabit/s ethernet. That is why Myrinet use x8 lanes for their 10 Gigabit/s cards which can do full wire rate to 9.6 measured throughput.
Notice that TERABIT cards would be 100x ie two orders of magnitude faster than this.
The most people currently have is slots of x16, although the PCIe spec allows for using x32 lanes.
Thus you will need some clever method if you want to interface a terabit dataflow to your machine (not to mention not bottlenecking it with interrupts).
One solution that gets a little closer may be Hypertransport which is available on a standardised HTX connector (as made on an Iwill board) from Hypertransport consortium. The HTX offers very low latency, but is still not into the terabit range. You would probably have to deserialise it and offload to several parallel subsidiary ASIC processors each on boards linked by say x8 or x16 PCIe, HTX or some future interconnect.
Standard PCI 33MHz, 32 bit transfers SIMPLEX and CONTESTED, even with minimal overhead like using burst transfers and DMA, could deliver 133MB/s of traffic.
Since one directional Gigabit ethernet is 1000/8=125MB/s of traffic, then you are wrong. PCI CANNOT KEEP UP WITH BIDIRECTIONAL GIGABIT TRAFFIC AT WIRE RATE. Consider that PCI is shared and you probably need the bus to take it somewhere eg disk or another card, and you just filled your bandwidth. Even going to the optional 66MHz speed (assuming all your cards support it) you still only have enough bandwidth to go to and from the NIC, and the rest of your system is saturated (unless you put other devices on a PCI bus of their own using some bridge arrangement on the motherboard. PCI-X is faster and can comfortably keep up with Gigabit flows but starts to peak out again by 10 Gigabit. Remember it's still not full duplex traffic simultaneously and that you have to leave some overhead for the pci bus commands like write, read, config etc.
The future is PCI Express and Hypertransport.
Terabit networking will not be with us for a LONG time ;-) I realise you probably MEANT to say 10 Gigabits.