The maximum number of sockets supported by a particular Windows Sockets service provider is implementation specific. An application should make no assumptions about the availability of a certain number of sockets. For more information on this topic see WSAStartup.
The maximum number of sockets that an application can actually use is independent of the number of sockets supported by a particular implementation. The maximum number of sockets that a Windows Sockets application can use is determined at compile time by the manifest constant FD_SETSIZE. This value is used in constructing the fd_set structures used in select. The default value in WINSOCK2.H is 64. If an application is designed to be capable of working with more than 64 sockets, the implementor should define the manifest FD_SETSIZE in every source file before including WINSOCK2.H. One way of doing this may be to include the definition within the compiler options in the makefile. For example, you could add "-DFD_SETSIZE=128" as an option to the compiler command line for Microsoft C. It must be emphasized that defining FD_SETSIZE as a particular value has no effect on the actual number of sockets provided by a Windows Sockets service provider.