I have an 800 Mbps cable internet plan and two computers connected by Ethernet. Speed tests show that both machines can reach roughly 500 Mbps, but their actual download speeds are very different: one gets around 300 Mbps while the other usually reaches only 70–80 Mbps. What could cause this difference?
3 Answers
Speed tests mainly show what the computers can get from the test server; they don’t guarantee that every download source will send data at that rate. Try downloading the same file from the same server on both machines, one at a time. If only one computer remains slow, investigate its adapter, cable, port, background activity, or security software. If both vary depending on the site, the remote server may be limiting the transfer.
Start by swapping the Ethernet cables and router or switch ports between the two computers. If the slow speed moves with the cable or port, that identifies the problem. If it stays with the same computer, check that machine’s Ethernet adapter and driver.
The slower computer may only have a 100 Mbps network adapter, or it could be connected through a 100 Mbps router or switch port. Check the negotiated link speed in the computer’s network settings. Older network cards and damaged cables can also fall back to 100 Mbps instead of gigabit.
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