<P> Several competitors of Digital Equipment Corporation such as Data General, Hewlett - Packard, and Computer Automation created their own operating systems . One such, "MAX III", was developed for Modular Computer Systems Modcomp II and Modcomp III computers . It was characterised by its target market being the industrial control market . The Fortran libraries included one that enabled access to measurement and control devices . </P> <P> IBM's key innovation in operating systems in this class (which they call "mid-range"), was their "CPF" for the System / 38 . This had capability - based addressing, used a machine interface architecture to isolate the application software and most of the operating system from hardware dependencies (including even such details as address size and register size) and included an integrated RDBMS . The succeeding OS / 400 for the AS / 400 has no files, only objects of different types and these objects persist in very large, flat virtual memory, called a single - level store . i5 / OS and later IBM i for the iSeries continue this line of operating system . </P> <P> The Unix operating system was developed at AT&T Bell Laboratories in the late 1960s, originally for the PDP - 7, and later for the PDP - 11 . Because it was essentially free in early editions, easily obtainable, and easily modified, it achieved wide acceptance . It also became a requirement within the Bell systems operating companies . Since it was written in the C language, when that language was ported to a new machine architecture, Unix was also able to be ported . This portability permitted it to become the choice for a second generation of minicomputers and the first generation of workstations . By widespread use it exemplified the idea of an operating system that was conceptually the same across various hardware platforms, and later became one of the roots of the free software and open source including GNU, Linux, and the Berkeley Software Distribution . Apple's macOS is also based on Unix via NeXTSTEP and FreeBSD . </P> <P> The Pick operating system was another operating system available on a wide variety of hardware brands . Commercially released in 1973 its core was a BASIC - like language called Data / BASIC and a SQL - style database manipulation language called ENGLISH . Licensed to a large variety of manufacturers and vendors, by the early 1980s observers saw the Pick operating system as a strong competitor to Unix . </P>

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