Abstract: A computer system, which is intended for easy introduction of architectures and fundamental softwares used by users, includes one or more first computers which implement the user interface function, one or more second computers which run application programs, and a third computer which administrates the first and second computers. A first computer turned on by a user operates on the third computer to assign a second computer for running a fundamental software which controls the execution of a user's application program. The assignment of a computer which runs the fundamental software for the user's application program at the time of user request facilitates the introduction, administration and operation of fundamental softwares and computers.