The MELCOM 81, which was announced in 1968, was not furnished with any kind of basic software that could be called an operating system. Instead, it relied on a programming environment (language system) that used a decimal machine language called COOL (standing for “Customer-Oriented Optimum Language”). Even after Mitsubishi Electric introduced its first operating system (AOS) in 1974 on the MELCOM 80 Model 31, the company continued to release subsequent office computers based on COOL until the MELCOM 80 models 18 and 28 in 1978.
The COOL system description that follows is based on the version supplied with the MELCOM 83 announced in 1969. The diagram below illustrates the MELCOM 83’s software system including COOL.