Maximum Number of Sockets an Application Can Use
http://support.microsoft.com/kb/111855/en-usThe maximum number of sockets that a Windows Sockets application can use is determined at compile time by the manifest constant FD_SETSIZE. To do this, from the Win32 SDK WINSOCK.H file:
This value is used in constructing the fd_set structures used in select(). The default value in WINSOCK.H is 64. If an application is designed to be capable of working with more than 64 sockets, define the manifest FD_SETSIZE in every source file before including WINSOCK.H. One way of doing this is to include the definition within the compiler options in the makefile, such as adding -DFD_SETSIZE=128 as an option to the compiler command line for Microsoft C.