The client versions of Windows are restricted in the number of half-open connections.
The 1010 limit for XPXP is well known, VistaVista has other limits depending on the version (e.g. Home BasicHome Basic has a limit of 22, UltimateUltimate has 2525). You
You can Google "Patch for Event ID 4226" to alleviate these limits. Post Vista SP2Vista SP2 the behavior is configurable through a registry key.
Windows ServerWindows Server can handle several tens of thousands of concurrent inbound connections given enough resources.
Depending on your server version, you have to change some default parameters to allow thisthese many connections to see this guide.
The author reports having seen 50.000+50.000+ concurrent connections to IIS6IIS6 on WS03SP1 x64WS03SP1 x64 with 4GB4GB RAM.