UNIX has long and interesting history. Having begun as the frivolous project of young researchers, UNIX became the mullions-strong industry. Now industry UNIX includes universities, multinational corporations, the governments and the international organizations of standardization.

UNIX has arisen in laboratory Bell Labs of firm AT&T more then 20 years ago. At that time Bell Labs was engaged in development Multiplexed Information and Computing Service (MULTICS) together with MIT and General Electric. But this system has failed because of too arrogant purposes mismatched a computers level of that time. Therefore Bell Labs in general has refused participation in project MULTICS that has enabled one of its researchers, Ken Thompson, to borrow in search work in a improvement direction of operating environment Bell Labs.

Thompson, and also employee Bell Labs Denis Ritchi and some other developed new file system which many features conducted the origin from MULTICS. For check of new file system Thompson has written a kernel of OS and some programs for computer GE-645 which worked under control of GECOS.

Ken Thompson had written by it even in days of work above MULTICS a game "Space Travel". It started it on computer GE-645, but it worked on not so well because of low efficiency of time division. Besides PC time GE-645 costed the expensive. As a result Thompson and Ritchi have decided to transfer game on costing in a corner without business PC PDP-7 of firm DEC having 4096 18-bit words, the teletype and the good graphic display. But at PDP-7 there was a unimportant software. Having finished carry of game, Thompson has decided to realize on PDP-7 file system above which it worked on GE-645.

From this work also there was first version UNIX though it and had no at that time any name. But it already included characteristic for UNIX: the file system based on index descriptors inode, a subsystem of management of processes and memory, and also allowed two users to work in a mode of time division. The system has been written on the assembler. Name UNIX (Uniplex Information and Computing Services) has been given to it by one more employee Bell Labs, Bryan Kerniganom who has originally named it UNICS, emphasizing its difference from multiuser MULTICS. Soon UNICS have started to name UNIX.

First users UNIX became employees of a patents department of Bell Labs who have found its convenient environment for creation of texts.

The big influence on destiny UNIX was rendered with its census in language of a high level C, developed by Denis Ritchi specially for these purposes. It has occured in 1973, UNIX totaled by this time already 25 installations, and in Bell Labs the special group of support UNIX has been created.

Wide circulation UNIX has received since 1974, after the description of this system Thompson and Ritchi in computer magazine CACM. UNIX has received a wide circulation at universities as for them it was delivered free of charge together with initial codes on of effective C-compilers has made UNIX unique the then OS because of an opportunity of carry on various computers. Universities have brought the significant contribution to improvement UNIX and its further popularization. One more step on a reception way of recognition UNIX as standardized environment became development of input-output library by Denis Ritchi stdio. Owing to use of this library for the C-compiler, programs for UNIX became easily transferable.

Fig. 5.1. History of development UNIX

Wide circulation UNIX has generated a problem of incompatibility of its numerous versions. It is obvious, that fact is rather unpleasant for the user, that the package bought for one version UNIX, refuses to work on other version UNIX. Attempts of standardization UNIX were periodically done, but they while made the limited success. Process of various versions UNIX rapproachement and their divergences has cyclic character. Before the person of new threat from any other operating system various manufacturers of UNIX-versions pull together the products, but then competitive struggle compels them to do original improvements and versions again miss. In this process there is also a positive party - occurrence of new ideas and the means improving as UNIX, and many other things the operating systems which have adopted at it for long years of its existence many useful.

The greatest distribution was received with two rather incompatible rulers of versions UNIX: AT&T - UNIX System V, and a version of university Berkeley-BSD. Many firms on the basis of these versions have developed and support versions UNIX: SunOS and Solaris by Sun Microsystems, UX by Hewlett-Packard, XENIX by Microsoft, AIX by IBM, UnixWare (sold now companies SCO), and this list it is possible to continue firms Novell long still.

The greatest influence on unification of versions UNIX such standards as SVID have rendered firms AT&T, POSIX, created under aegis IEEE, and XPG4 consortium X/Open. In these standards requirements to the interface between applications are formulated and OS that enables applications successfully to work under control of various versions UNIX.

Irrespective of the version, the general for UNIX features are:

• The multiuser mode with means of data protection from not authorized access;
• Realization of multiprogram processing in a mode of time division, based on use of algorithms preemptive multitasking;
• Use of virtual memory mechanisms and swapping for increase of multiprogramming level;
• Unification of input-output operations on the basis of expanded use of concept "file";
• The hierarchical file system forming a uniform catalog tree irrespective of physical devices quantity, files used for accommodation;
• Bearableness of system due to a writing of its basic part in language C;
• Various means of processes interaction, including through a network;
• Cash a disk for reduction of average time of access to files.