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What are UNIX, POSIX and SUS Concepts?

by elitelaunch
UNIX, POSIX ve SUS kavramları nedir?

The duo that made UNIX and the C language possible: Ken Thompson and Dennis Ritchie.

In this article, we’ll take a look at what UNIX is, its historical development, and some of the standards found in most operating systems based on the UNIX philosophy.

UNIX… It is a concept that people who program in languages ​​that are inferior to other modern programming languages, such as C and C ++, often face. So what is this UNIX?

History of UNIX and the C language

UNIX was originally founded in 1969 by AT&T. In bell labs Developed for PDP-7 machines operating system. Firstly Assembly language of PDP-7 written with. As the name, UNIX was put to evoke MULTICS. MULTICS, on the other hand, was a system developed by AT & T together with MIT and General Electric, but later AT&T was removed from the project. As it is not an economical operating system withdrew. Ken Thompson incorporated several ideas inspired by the MULTICS operating system into UNIX; file system in tree view, separate program for command processing (shellWe are talking about ideas like).

UNIX operating system in 1970 for PDP-11 machines Assembly language of PDP-11 with rewritten. In fact, most of the traces of the PDP-11 are today In UNIX implementation, even the most used UNIX implementation On Linux even possible to see.

Logo of the C programming language.

After a short time Ken thompson‘s colleague and one of the producers of UNIX Dennis Ritchie, C language revealed. The C language was inspired by the B language and the B language from the BCPL language. In 1973, the C language matured and UNIX a language that can be almost completely rewritten became. UNIX operating system so Written using high-level language first OS and port UNIX to other hardware much easier it has become an operation. In order to run an open source UNIX implementation written in C language, you can use compiler, linker and assembler programs written only for the ISA of the target processor. to machine language you need to translate.

This method is still modern operating systems continues to be valid on. Having a small or large Assembly code still in every operating system has toBecause code written in high-level languages ​​(including the code of the system kernel) thinks that memory is prepared accordingly; and Assembly language, this the possibility to prepare the memory presents us.

The emergence of standards such as POSIX and SUS

A logo of POSIX.

POSIX (Portable Operating System Interface for UNIX)Was founded in 1988 with the aim of providing software unity between UNIX implementations. IEEE (Institute of Electrical and Electronics Engineers) It is a standard created by. Operating systems with POSIX API “POSIX compatible operating systemIt is called.

POSIX API; originally UNIX to system calls and C standard library is based. This means that other operating systems can be ported freely. However, it can work on other operating systems with a few small touches to the POSIX library. For example with socket programming on Winsock 2 POSIX supported UNIX systems on you “Berkeley SocketsSocket programming on ” is almost the same from the eyes of the programmer the main difference exist. For example, Berkeley Socketsis one of the main ideas of UNIX. the view that everything is file are available. For this reason Berkeley Sockets A socket created with its own “file descriptorBut in Winsock 2 this situation it is different.

Logo belonging to Single UNIX Specification (SUS).

Novell, when the calendars show the year 1993, UNIX rights He bought it from AT&T. Just a year later, UNIX rights were established by European UNIX system manufacturers in 1984. To X / Open and left the UNIX job. Later X / Open, UNIX trade right pass some tests decided to give it to operating systems. In these tests, compatibility with UNIX is measured and according to the degree of compatibility, the target operating system To the basic philosophies of UNIX While the decision is made at multiple points depending on how well it fits or not, the target operating system basic environment, network configuration, window system, C language support things like being tested. This test family of standards Single UNIX Specification (SUS) It is called. SUS has 5 certification labels:

  • UNIX 93,
  • UNIX 95 (SUSv1),
  • UNIX 98 (SUSv2),
  • UNIX 03 (SUSv3),
  • UNIX V7 (SUSv4).

Few BSD and Linux distributions have been able to pass these tests, because the goal of these distributions was to achieve POSIX compatibility.

X / Open, in 1996 Open Software Foundation (OSF) combined with The Open GroupHe founded. Interested in UNIX almost all organizations, The Open Group is a member of and the development of UNIX API and standards is still today, the Open Group, IEEE and ISO are partners. The Austin Group Continues by.

Comparison of POSIX and SUS: While POSIX compatibility only looks at the bottom part, everything in the visual is tested in SUS tests.

POSIX compatibility of an operating system, as we mentioned when describing POSIX, is only possible with the target operating system’s POSIX API. how compatible you are and POSIX-based software on that operating system is it working? While expressing, SUS compatibility is the target operating system, Which UNIX standard meets is a label that indicates. For example, to the Windows operating system POSIX while semi-harmonious, SUS no standard not suitable. Because Windows is not a UNIX-based operating system, but the POSIX standards some of them meets. If you want to keep completely POSIX compliance in your system, Windows Subsystem for Linux (WSL) You can achieve this harmony using.

One UNIX variantprograms that belong to other UNIX variants, although they are compatible with POSIX or even SUS. may not work. Linux applications, for example, in most UNIX variants does not run or compile. Although Linux is a UNIX variant, it is different from UNIX on it. system calls, libraries, structures There are special things like. Therefore; If an application developer wants portability in their application, they must comply with the POSIX or SUS standards. adhere to will be better.


UNIX operating system’s contributions to the computer world too much it is an indisputable fact. Including Technopat server, Most servers in the internet world, one UNIX implementation with (usually Linux). Similarly, in our mobile phones operating systems they are all UNIX implementations. As such, Learning about UNIX it could be a beautiful thing.

You can indicate what you want to add or your opinion about the article in the comments, and use Technopat Sosyal to ask a question in your mind.

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