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Gigabit Ethernet: a buyer’s guide

Manek Dubash ZDNet.co.uk

Published: 08 Dec 2003

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Benchmarks

Gigabit Ethernet cannot offer the full 1000Mbps (1Gbps) on a standard PC largely because a standard PC uses a 33MHz 32-bit PCI bus through which all data traffic passes. Gigabit Ethernet’s maximum theoretical throughput is 132MB/s (which is about 1Gbps). In practice, you're more likely to see a doubling or three-fold speed increase over a 100Mbps network because of delays introduced by latency and interrupts, and because data destined for the network must cross the bus twice -- from disk to CPU and memory, and back to the network controller. Also, no single disk mechanism can sustain a throughput high enough to saturate a gigabit pipe.

Synthetic benchmarks from SiSoft Sandra showed a maximum transfer rate of 14MB/s -- about twice that of the 100Mbps networking components. A real-world test involving multiple copying of a 1.4GB file (big enough to defeat the RAM cache) and averaging the times highlighted few product differences. For the record, the average time taken to transfer the file dropped from 226 seconds at 100Mbps to 106 seconds at 1000Mbps.

CPU usage was similar too, since all the cards perform TCP/IP checksum processing. We found that activating this option cut CPU usage by 3-5 per cent. However, the 64-bit cards also allow you to select non-standard Ethernet frame sizes, and boosting it to Alteon's 'jumbo frame' size of 9Kbit should cut the IP processing overhead even further.

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