I upgraded my broadband to 900/100 Mbps, and three Android phones—two Pixel 6s and one Pixel 8—consistently reach around 900 Mbps download and 100 Mbps upload. However, three Windows 11 laptops, including a newer Microsoft Surface Laptop 6, a two-year-old Dell, and a six-year-old HP, all plateau at roughly 320–330 Mbps.
The same limit appears over both Ethernet and Wi-Fi. Ethernet negotiates at 1 Gbps, while Wi-Fi shows a 6 GHz connection with a 2402 Mbps transmit/receive link rate. TCP auto-tuning is set to Normal and Receive Segment Coalescing is enabled. I have repeated tests using Ookla, BT's speed test, Fast.com, and Cloudflare, with nearly identical results each time. Latency is around 12 ms with no packet loss.
What could cause all three Windows laptops to hit almost exactly the same speed limit when the Android phones reach the full broadband speed?
1 Answer
Check Windows TCP receive-window auto-tuning from an elevated Command Prompt with `netsh interface tcp show global`. If the setting is disabled, Windows can restrict throughput. It should normally show `Receive Window Auto-Tuning Level : normal`; if needed, set it with `netsh int tcp set global autotuninglevel=normal`. Since yours is already set to Normal, the next useful test would be booting one laptop from a Linux live USB and running a speed test. If Linux reaches much higher speeds, that would confirm a Windows software or driver issue rather than a broadband problem.
Auto-tuning already reports Normal. The phones prove the broadband connection can reach the advertised speed, while every Windows laptop hits the same ceiling, so I suspect a negotiation, driver, or Windows networking issue.