The MELCOM81 office computer was first marketed in 1968. It was developed by Mitsubishi Electric in response to the rapid dissemination of clerical work automation and rationalization from large companies to small/mid-size companies. It was designed as a computer suitable for small and mid-size companies, and also as a computer which could be used as a terminal processor for computer systems at large companies.
The phrase "office computer" was used in the MELCOM81 catalog, and this became the source of the standard category name of this type of computers in Japan.
The arithmetic unit was the 1-bit type, equipped with a decimal correction function similar to that of an electronic pocket calculator, and was comprised of transistors and diodes. By developing a low-cost, high-reliability, compact magnetic disk memory unit, with a maximum of 12,000 digits of memory, the MELCOM81 was able to classify and tabulate multiple items, and perform many types of job processing. In order to compensate for the lower speed of the magnetic disk, Mitsubishi Electric developed an easy-to-understand, high-productivity machine language (COOL) having features of decimal memory addressing, binary coded decimal arithmetic with words comprised of 12 digits and a sign, a 3-address control system, and compound instructions for completing clerical work operations with a single instruction.
The development of an innovative photoelectric carriage control system made it possible to completely convert carriage control to the stored program system and to move the 620mm-size platen freely, so it was easy to perform continuous vertical printing as well as effective ledger and table generation, and it also eliminated the need for a mechanical tab setting.