POSIX (portable open system interface for UNIX) is a range of UNIX-based standards which ensure the compatibility and interoperability of applications in a heterogeneous network. A heterogeneous network consists of computers from different manufacturers, as well as system and application software from different software suppliers.
The POSIX standard was defined as the national American standard by the Institute of Electrical and Electronics Engineers (IEEE) in 1989. It was then extended by the X/OPEN consortium, and in 1990 became adopted as the international standard.
(X/OPEN Portability Guide IV).
The X/OPEN Portability Guide IV, also known as XPG4 standard, comprises 7 volumes, including interface definitions for basic operating systems, programming languages, data management and networking. The BS2000/OSD operating system as of V2.0 supports the XPG4 standards which are contained in the first two volumes:
Volume 1: System Interfaces and Headers (approx. 350 program interfaces)
Volume 2: Commands and Utilities (approx. 200 user interfaces)
In order to support these interfaces, the POSIX functionality was integrated into BS2000. POSIX designates both the IEEE standard and the BS2000 “POSIX” functionality. POSIX satisfies the requirements to allow its certification according to the XPG4 standard, which is carried out in two stages: at the end of 1995, BS2000 received the “XPG4 base branding” (XPG4) from “The Open Group” (previously X/OPEN), and around mid 1997 it received branding according to the “XPG4 UNIX profile” (also known as XPG4.2 or UNIX95). In addition, BS2000 with its POSIX subsystem has been certified as an internet server by “The Open Group” in 1999.
The kernel of the POSIX software product is implemented as a BS2000 subsystem. The library functions of the XPG4 standard are available to the user via a C library, and a defined set of commands is available via a shell (POSIX shell). The C library is a component of the product CRTE (Common RunTime Environment).
Application programs can be easily ported with POSIX, irrespective of the operating system being used. Programs consistent with XPG4 can therefore also run in BS2000 following recompilation.
POSIX program interfaces are offered together with BS2000 program interfaces. It is possible to use a combination of both BS2000 and POSIX program interfaces in the same program, albeit with certain restrictions.