The TCP Analyzer reads the TCP Window (RWIN) value from actual TCP/IP packet headers during the TCP handshake between you and our server. It does not read Registry values. With that in mind, what the Analyzer displays is what your client advertises to other web servers.
Some modern Operating systems (Linux, Windows 7, Vista) have auto-tuning algorithms for the TCP Receive Window (RWIN) value. Under those OSes, a small RWIN value is advertised by the client first, but then it changes with each packet until it settles to a larger value to accomodate broadband transfers. Those OSes can still be tweaked as described in our tweaking articles, and are still supported by our free tweaking software, the TCP Optimizer. However, under Windows 7/Vista, you may not be able to set a fixed RWIN value directly.
Google Chrome is the only known browser that can also modify the TCP Window for sockets it creates under some OSes, and therefore servers may not get your corret RWIN value. We've confirmed that Chrome changes the advertised RWIN under some versions of Windows XP and Windows 2003. If the RWIN value seems wrong under Chrome, you may want to test with a different browser. (See:
issue ID 6356)
