In this study, a distributed file system is constructed among several computers which operate under UNIX compatible operating system named RTDFS UNIX. The main features of RTDFS UNIX are the abilities providing file access transparency and appropriate time-response for real-time applications. The ability of file access transparency allows all users to access files located in any machine with the same method as the local machine on which he logged. This feature can be achieved through extending UNIX naming tree, that is, including all files existing in all machines on the network in a single hierarchical naming tree, and inserting the communication layer in the operating system kernel. A message has a priority and real-time flag, and all messages are sorted according to their priorities for the order of service. Real-time request is served first of all, and all nonreal-time requests are served in the order of the priorities. Real-time process which is a server for real-time request, has privilege in gaining CPU control and accessing a disc block, and it is loaded in core memory until disappearing from the process table. There are two time intervals for process switching, one for real-time services and the other for nonreal-time services. If there are real-time processes in process table it is reduced to 40 milli-seconds to prevent them from waiting too long. Otherwise, it is the same as UNIX, i.e. one second, because frequent process switching causes time overhead. All informations about naming tree and addresses of machines, are contained on a file named "/etc/nettree". Thus it is very easy to change or add machines in the naming tree.