Mitsubishi Electric’s operating systems for office computers can be divided into three generations.
The first generation, which arrived prior to the systemization of software as an operating system, was a programming environment (a programming language system) called COOL (standing for “Customer-Oriented Optimum Language”), a decimal machine language. COOL was first installed on the MELCOM 81, Mitsubishi Electric’s first office computer announced in 1968. Even after operating systems appeared on office computers, subsequent COOL-based office computers were rolled out, and COOL was used until the MELCOM 80 models 18 and 28, announced in 1978.
The second generation, consisting of 16-bit operating systems, first appeared on the MELCOM 80 Model 31, announced in 1974. The first of this generation was a single-task operating system called AOS (which stood for “All-round Operating System”), but later Mitsubishi Electric developed DPS (which stood for “Dynamic Processing System”), a multitask version of AOS, for the Model 38, which was announced in 1977. Users were able to select either AOS or DPS depending on their machine’s configuration.
The third generation consisted of 32-bit operating systems and first appeared on the MELCOM 80 OFFICELAND series of office computers, which were announced in 1982 and 1983. Called DPS 10, this operating system was based on UNIX System III with the extended functionality required for business computers. Later, in response to the first wave of open systems, Mitsubishi Electric released the DP-UX operating system for the RX7000 series of Solutions Servers that were announced in July 1994. DP-UX featured much better connectivity with personal computers and UNIX machines and more powerful functions that handled various de facto standards.