A host data processing system operating under the control of a host operating system such as an enhanced version of the UNIX operating system on a RISC based hardware platform includes an emulator which runs as an application process for executing emulated system (ES) user application programs. The emulator includes a number of emulated system executive service components including a socket command handler unit and a socket library component operating in shared memory and an interpreter, an emulator monitor call unit (EMCU) and a number of server components operating in host memory. The host operating system further includes a host socket library interface layer (API) which operatively connects through a TCP/IP network protocol stack to the communications facilities of the hardware platform. The socket server components operatively connect ES TCP/IP application programs to the socket library interface layer of the host operating system when such application programs issue standard ES socket library calls. The socket command handler unit maps the ES socket library calls into appropriate input/output requests directed to the EMCU. The EMCU directs the requests to an appropriate socket server component which in turn issues the appropriate host socket library calls to the host socket interface layer thereby eliminating both the need to communicate through additional protocol stacks and to provide additional communication hardware facilities.