Member Avatar for HpGdfs47iOT

Hello,
Does anyone out there fully understand the Gigabit network adapters.I have been doing some reading to try and make an informed purchase but am getting a bit confused with what I think is people using incorrect terms in their MBps v's Mbps etc or me just going into information overload.
From what I have read it would seem that PCI gigabit adapters are actually a bit of a mis-nomer as the PCI bus cannot support such volumes of information ? I may well have it all wrong but if the 32 bit bus will accomodate 133MB/s or at best in full duplex 64 bit-266MB/s wouldnt this mean that it could not transfer the full gigabyte/sec to the CPU through the parallel port?:confused:
I hope some one out there has a better grasp on the terminology and values and can sort me out please.
Thankyou,
Kind Regards

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Short version first: Mbps = megabits per second, MBps = megabytes per second (1 Gbit/s = 1,000,000,000 bits/s = 125,000,000 bytes/s = 125 MB/s, about 119 MiB/s). Protocol overhead and frame gaps reduce what a TCP stream actually delivers on a 1 Gbps Ethernet link, so you typically see ~940 Mbps in clean tests. See Gigabit Ethernet.

On the bus question: legacy PCI is a shared parallel bus and was not designed as a point-to-point pipe for multi-gigabit full-duplex traffic. Network cards avoid copying every packet through the CPU by using bus mastering / DMA to place packets directly into RAM, but the overall topology, arbitration, interrupts and host bridge crossings still limit sustained bidirectional throughput. For background, read PCI (computer bus) and Direct memory access.

Why servers use PCIe: PCI Express is point-to-point and gives per-lane bidirectional bandwidth (Gen1/2/3 lane rates scale up), so even small PCIe links usually have more headroom than old PCI. That is why modern NICs and server cards move to PCIe or to faster links like 10 GbE when needed. See PCI Express.

Practical buying and troubleshooting tips: for a single desktop link a PCIe x1 gigabit adapter is inexpensive and fine; for heavy simultaneous traffic choose higher-lane PCIe or 10 GbE. Verify switch port negotiation, use Cat5e/Cat6 and a true gigabit switch (1000BASE-T), enable hardware offloads/jumbo frames only when supported end-to-end, and measure with tools like iperf to see real TCP throughput (iperf). As noted, unit confusion is common; is right that servers favor PCIe for bandwidth.

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Member Avatar for jbennet

Yeah i dont think gigabit pci cards can do the full gigabyte, because of the latency of other system components (hell, no hard disks can do 1gb a second writes anyway, so it wont matter for downloading)

Most of the time i see them in servers, they are PCI-Express instead, which i guess helps them use more of the bandwidth.

Member Avatar for ber2020

your right bro... :)

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