By default the number of simultaneous connections to a HTTP 1.0 server is 4, to a HTTP 1.1 server is 2.

To change these limits, use Regedt32 to navigate to:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings

On the Edit menu, add the following REG_DWORD value names:

MaxConnectionsPerServer - The number of simultaneous requests to a single HTTP 1.1 Server. The default is 2.

MaxConnectionsPer1_0Server - The number of simultaneous requests to a single HTTP 1.0 Server. The default is 4.

NOTE: Increasing these defaults is a violation of the HTTP protocol, and should only be performed if absolutely necessary.