<p>A control unit for controlling an automobile has a one-chip microcomputer including an internal memory (2) for storing an operating program and an application program. An external memory (7) is connected to the one-chip microcomputer which stores an additional application program. By such an expedient the one-chip computer can be readily installed in another type of automobile thereby eliminating the necessity of development of an updated application program in the one-chip microcomputer. In a further aspect of this invention, a control unit for an automobile has a one-chip microcomputer including a cache memory (19) and an internal memory (2) which stores an operating system program and an application program. An external memory (7) is connected to the one-chip microcomputer for storing an additional application program whereby the additional application program stored in the external memory (7) is fetched into the cache memory (19) for execution. Such an arrangement has the advantage of real time processing.</p>
