History of Hitachi Operating Systems

　 In the era of early computers such as HIPAC 101, HITAC 301 and HITAC 301，HIPAC 103, from the 1950s to early 1960s, nothing equivalent to an operating system existed. In those days, programs, such as symbol input routines, interpreters and function libraries, were individually provided as software. Symbol input routines converted programs into machine languages by inputting them from punch cards or paper tapes, and interpreters executed pseudo instructions while converting them into machine languages.
　 Hitachi's first full-scale OS was developed in 1964 for HITAC 5020. At that time, the term "operating system" was not really in general use, and OSs were usually called "monitor systems." The monitor systems were divided into a system monitor that was concerned with the whole system, such as I/O operation of peripherals, allocation of I/O devices and protection of the monitor routine, and a job monitor that controlled continuous processing of each job in internal processing.
　 The term "OS" began to be used with the introduction of the HITAC 8000 series of medium to large general-purpose computers , which were developed based on a technical collaboration with RCA in 1965, plus Hitachi’s unique technology. For this series, Hitachi first introduced the OSs POS (Primary OS), TOS (Tape OS) and TDOS (Tape Disk OS) from RCA, and subsequently developed DOS, EDOS and EDOS-MSO based on those OSs. EDOS-MSO, the final OS for the HITAC 8000 series, was capable of simultaneously performing large-scale batch processing, large-scale online processing and remote batch processing, and supported features such as storage management using a multi-stage method and automatic disk file allocation.
　 OS7, which was developed in 1970 as the OS for HITAC 8700/8800, was a full-scale large software system that supported a virtual space and multiple processors. At that time, it ranked among the world’s largest OSs.
　NDOS, released in 1972, was the OS for HITAC 8250, and was developed for users of small to medium computers with main storage sizes mainly ranging between 32 KB and 64 KB.
　From 1974, the VOS (Virtual Operating System) series was Hitachi's mainstay OS for HITAC M series computers. VOS2, developed in 1974, was the first VOS series OS. VOS2 was equipped with functions such as virtual storage of up to 16 MB, a new virtual storage access method, a real-time processing function based on control programs, and an enhanced range of language processors.
　From 1975, the VOS series was divided into small to medium OSs and large OSs. In 1975, Hitachi developed VOS1 mainly for users of small to medium computers of the M series as the successor OS to NDOS. VOS1 supported a virtual storage function and the virtual storage access method VSAM based on the technologies of NDOS, and supported various use applications including batch processing, online processing and remote batch processing. Small to medium OSs were subsequently divided into the VOS0 series for users of small computers and the VOS1 series, which also supported users of medium computers.
　 VOS0, which began shipping in 1979 as the OS for the HITAC L series of distributed-processing computers, was the first VOS0 series OS. VOS0/ES, released in 1983 as the successor to VOS0, was developed with the aim of increasing the efficiency of office operations in each division, reducing development/operation costs and establishing an organic coupling with other systems.
　VOS K, which began shipping in 1988 as the successor to VOS0/ES, placed top priority on ease of use and high speed in order to enable operation by personnel with no professional computer know-how who were working in practical business divisions. It was promoted with the catchphrase: "The YES computer" (Y: do it Yourself; E: Easy to use; S: high Speed).
　To continue the VOS1 series of OSs following the release of VOS1, Hitachi started shipping VOS1/ES in 1983 and VOS1/ES2 in 1988. VOS1/ES realized enhanced functions such as micro mainframe coupling and multimedia processing. VOS1/ES2, the successor to VOS1/ES, maintained continuity from VOS1/ES, and achieved advanced distributed processing functions such as Distributed Department Computer Connection (DDC) that linked dispersed departmental computers with the host computer, a slip data distribution/processing system (Form-MMC) and an extended host access function.
　 As regards large OSs, Hitachi started shipping VOS3, which was the highest-level OS in the M series, in 1977. VOS3 featured functions required for large OSs, such as multiple virtual storage, multiprocessor function, centralized resource management function, strengthened RASIS functions and TSS processing function.
　 In 1982, Hitachi started shipping VOS3/SP, which was designed as an extension of VOS3 with large-capacity disk support, channel extension, etc. While VOS3 was free software bundled with hardware, VOS3/SP and later OSs were paid program products. In 1984, Hitachi started shipping VOS3/ES1, which supported a 31-bit extended addressing mechanism. With the 31-bit addressing support, VOS3/ES1 extended a 16-MB virtual address space to 2 GB. In 1990, Hitachi started shipping VOS3/AS, which supported the M/ASA architecture that had a data space and a Super space capable of addressing up to 16 terabytes, beyond the 2-gigabyte address space.
　 In 1979, Hitachi developed VMS, which was a virtual computer system that generated multiple virtual computers (VM: Virtual Machine) on one real computer, and enabled each OS to operate independently on the respective VM. In 1985, Hitachi completed VMS/ES which supported the M series’ extended addressing function and enabled VOS3/ES1 to be executed as an enhanced version of VMS. VMS/AS, a virtual computer system that enabled VOS3/AS to be executed, was completed in 1990.