Unix

UNIX™ is the name of a Operating system Multitâche and Multiutilisateur created in 1969, of mainly professional use, conceptually open and based on an approach by which it offers many small tools each one equipped with a specific mission. It gave rise to a family of systems, whose most popular In 2007 is Linux and Mac OS X. One names family Unix the whole of these systems. It is still said that they are of standard Unix and they are qualified Unices . There exists today a whole of standards joined together under the standard POSIX which aims at unifying certain aspects of their operation.

Work stations and Unix waiters

Only some large manufacturers of Work stations and waiters developing derivatives of UNIX remain In 2007  :

Microsoft had some time the rights of a version of UNIX which named XENIX.

The philosophy of the manufacturers of stations and UNIX waiters was at the beginning to develop an operating system to be able to sell their machines, by adding small if possible to it “more” to dissociate competition. It was to forget that the UNIX parks are generally heterogeneous and that any difference from one machine to another, even created with the best intention of the world, thus threatens interworking constitutes a real risk of against-productivity because force the data processing specialists to arrange in order to inter-connect the systems.

It is one of the reasons for which many these manufacturers propose from now on the GNU/Linux system with their waiters. However, if the core Linux is well defined, the system Linux appreciably changes from one distribution to another, which leads to dissimilarities causing waste of time sometimes.

This problem arose already formerly with the opposition between UNIX System V and UNIX BSD, in particular on managements appreciably different from the Impression and signals.

The UNIX system

The UNIX system is Multi-utilisateur and Multitâche, it thus allows a mono computer or multiprocessors to carry out apparently simultaneously several programs in protected areas belonging each one to a user.

Genesis of UNIX

In 1969, Ken Thompson developed the first version of an operating system mono-user under the name of " New Ken' S System". It completed this work on a Mini-ordinateur PDP-7 ( Programmed Data Processor ) of mark DEC animated by GECOS and wrote the new software in Assembly language. The name Unics was suggested by Brian Kernighan following a pun " latin" with Multics; " Multi- because Multics made the same thing in several ways whereas Unics made each thing of only one façon". This name was contracted thereafter in Unix (for with the final being deposited under the name UNIX by AT&T), however nobody does not remember who is at the origin of the modification of the " cs" in " x".

In 1971, conscious of the difficulty which the maintenance of a system written in assembly language represents, Ken Thompson thought of rewriting UNIX in TMG; However it found that TMG did not offer that which it needed; for one short period he thought of rewriting UNIX in FORTRAN but finally conceived the B with the assistance of Refusals Ritchie (1969-1970), while taking as a starting point the language BCPL. However UNIX was never rewritten out of B; B did not support a " types" , all the variables were same size as the words ( Word ) of architecture, the arithmetic one on the floating ones was not really implemented; moreover the compiler B used the technique of the " threaded code". This is why Dennis Ritchie undertook in 1971 NB (New B), which was famous in C, while starting by creating types; it was joined by Alan Snyder, Steven C. Johnson, Michael Lesk and Ken Thompson in order to continue the modifications until 1977. Unix was thus carried out of C.

The expansion

A decree going back to 1956 prohibited with at&T company, on which Bell Labs depended, to market another thing that telephone or telegraphic equipment. This is why the decision was made in 1973 to distribute the complete UNIX system with its source code in the universities to educational ends, with the help of the acquisition of a license at the very weak price.

In 1975, starting from version 6 of the system, UNIX was diffused out of the Bell laboratories. When in 1979 it reaches its version 7, the evolution was accompanied by many notable modifications such as the extension to 2 Go of the maximum size of a file, the addition of several utilities, and especially the portability of the system. It is at that time that the first large bearing of UNIX, the version 32/V, was carried out, on a VAX 11/780.

As of the end of the year 1977, researchers of the University of California made many improvements to the UNIX system provided by AT&T and distributed it under the name of Berkeley Software Distribution (or BSD). Thus BSD was for example the first UNIX system to exploit fully the mechanism of paginated virtual Memory of VAX 11/780.

Three branches of development of the sources transfer the day:

  • the branch of search for AT&T which developed, always at the Bell laboratories, until 1990, 8th, 9th and 10th editions of the UNIX system.

  • the commercial branch of AT&T which developed System III, then four editions of System V (System V, SVR2, SVR3, SVR4).
  • Berkeley Software Distribution developed by the the University of California, until 1994.

It will be noted that these branches mutually borrowed code and/or concepts. As follows:

  • the 8th edition is resulting from the version 4.1 BSD.

  • version SVR3 borrowed the concept of the STREAMS from the 8th edition.
  • version SVR4 integrated much code of the version 4.3 BSD.
  • the version 4.4 BSD comprises very an minor amount of code of version SVR4.

UNIX owners

Since 1977, AT&T placed the sources of UNIX at the disposal of the other companies, so that a great number of derived from UNIX were developed:

  • XENIX, founded on the 7th edition developed in 1980 by Microsoft.

  • AIX, developed by IBM, whose first version of 1986 was based on System V release 2.
  • Solaris, developed by Sun Microsystems, based at the beginning on BSD 4.1c, then on System V release 4 (SVR4).
  • HP-UX, founded on System V, developed starting from 1986 by Hewlett Packard
  • Ultrix, developed by DEC. The Ultrix-11 version, intended for the machines of family PDP-11, is based on the 7th edition, with additions coming from System V and BSD. The Ultrix-32 version, intended for the machines of family VAX, is primarily founded on BSD.
  • IRIX, developed by SGI.
  • UnixWare, descendant of SVR4, developed by Novell then resold with SCO Group.
  • SCO Group UNIX, founded on XENIX and System V developed as of 1979 by Santa Cruz Operations and Hewlett Packard.
  • Tru64, founded on a version of the micronucleus Mach 2.5 realized by consortium OSF (Open Foundation Software). It was initially developed under name OSF/1 then DEC UNIX by Digital Equipment Corporation, Compaq and finally Hewlett Packard.
  • A/UX, an UNIX developed by Apple, compatible with Mac OS.

In 1982, AT&T announced the support of its product, the version System III, which constitutes of this fact its first commercial release of UNIX. In 1983 followed the version System V.

Minix, XINU and Linux

In 1985, an American professor domiciled in the Netherlands, Andrew S. Tanenbaum, developed a minimal operating system, baptized Minix, in order to teach the concepts of the operating systems to its students. A similar project named XINU (for Xinu Is Not Unix ) made also its appearance in the years 1980 pennies the direction of Douglas Comer.

In 1991 a Finnish student, Linus Torvalds, decided to conceive, on the model of Minix, an operating system able to function on architectures containing processor Intel 80386. The core, which was then at the experimental stage, was to be generated on a system Minix.

Linus baptized its system Freax and posted the following message on the newsgroup comp.os.minix:

Hello everybody out there using minix - I' m doing has (free) operating system (just has hobby, won' T Be big and professional like gnu) for 386 (486) AT clones.

The name of “Linux” comes in fact from the person who lodged the project for her diffusion (version 0.0.1) and not of an egocentric person choice of Linus. He wanted a time to rename his system Freax , but he was too late, Linux had already been essential near the aficionados. Linux does not contain a code coming from UNIX, but it is a system inspired of UNIX and completely rewritten. In addition, Linux is a Free software.

Mac OS X

Unix is at the origin of Mac OS X, the current version of the operating system of Apple. Mac OS X is based on the same core as MkLinux, Darwin, and XNU: a micronucleus Mach. However, the layer Unix de MacOSX (a FreeBSD modified) is not a personality of the core Mach, integration is more subtle since it is connected rather with a Clerc's Office of the one on the other.

At present

Here a nonexhaustive diagram recalling overall the appearance of the principal systems of the UNIX type:

The incompatibility growing between the many alternatives of UNIX proposed by the various editors for the various machines ended up attacking the popularity of UNIX. Nowadays, the systems UNIX owners, a long time majority in industry and education, are less and less used. On the other hand, three systems of the UNIX type based on BSD (FreeBSD, NetBSD and OpenBSD) on the one hand, and the system GNU/Linux, compatible UNIX, on the other hand, like Mac OS X (based on Darwin), occupy an increasingly important market share.

The UNIX standard

The great number of UNIX systems developed on the basis of System V of AT&T or of BSD led members of the user group /usr/group , which took since the name of UniForum, to forge an UNIX standard as of 1981 in order to ensure a maximum portability between the various systems:

  • in 1984 the group /usr/group publishes POSIX, a series of standards developed under cover of the IEEE ( Institute off Electrical and Electronics Engineers ). POSIX is thus also known under the name IEEE P1003.

  • in 1985, AT&T publishes SVID ( System V Interfaces Definition) describing System V. This first definition is different from POSIX.
  • at the same time, a consortium of manufacturers (Sun, IBM, HP, DEC, AT&T, Unisys, ICL, etc) publishes the standard X/Open Portability Guide Resulting 3 (XPG3). This standard deals particularly with the differences resulting from geographical location (date, alphabet, etc).

Technical sides

The core of UNIX rests on four elementary concepts: the files, the process, IPC (communications inter-process), and the rights of access:

Files

The file is the basic unit of management of resources under UNIX. File under UNIX is not typified, which wants to say that the system does not know the format of the data which it contains, and can represent various resources such as a succession of characters stored on a physical support, a peripheral (hard drive, printer, uncurler with bands, memory, interface network etc), or even of the parameters dynamically reconfigurable of the core. A file is an object referred in a Filesystem. This reference contains all the necessary informations with the treatment of this file: owner, group (each file being held by an owner belonging to one or more groups, the owner and each group have specific rights), rights of access of the various categories of users, cuts, date of last modification, dates from the last access, references of the storage blocks on the disc if it represents a succession of characters.

Process

The process is the basic unit of management of the treatments under UNIX. It is about an abstraction including/understanding a space of addressing and supporting one or more floods of execution of program, the Thread S, each one having a pile and its own context of execution. UNIX being a Multi-task system , it allows to share the resources of calculation between the threads. In addition it is Préemptif, which implies that this division is carried out in a transparent way for the threads. This transparent division is carried out thanks to a ordonnancor adapted with use for which the system is intended. In a system at time-sharing, the ordonnancor tries to distribute the resources of calculation in an equitable way between the threads while privileging the response time of the inputs/outputs. In a system time-reality, the threads are scheduled according to temporal constraints which must be guaranteed strictly (hard time-reality) or with a certain rate of failure (flexible time-reality).

Communications inter-process (IPC)

The communications inter-process are used to arbitrate the use of resources shared between various processes or threads by the means of objects of synchronization such as the semaphores or the mutex, to allow the control of a process by another or by the core by the means of signals, and finally to make it possible two processes to establish a communication: locally by the means of pipes, segments of shared memory or files of messages, and a transparent way (locally or on a network) by the means of sockets.

Access control to the resources

At the software level, the Security policy of the UNIX system is founded on the principle which each resource admits an identifier, an owner and a whole of rights of access (in reading, writing, execution) divided into three groups: 1) rights of the owner; 2) rights of the group to which the owner belongs; 3) rights of the other users. The majority of the current UNIX systems propose a finer model, that of the access control lists (ACL - Access Control List). A special user called root has all the rights on all the resources. He is in general used only for tasks of administration. By preoccupation with a better safety, certain UNIX systems make it possible to better moderate the acquisition of additional rights by the users. Thus Linux proposes it the “capacities” (capabilities) and Mac OS X makes it possible to install applications and to intervene on the system requirements by means of an account administrator distinct from root (which is decontaminated besides by defect), in what it cannot modify the fundamental files of the system.

At the material level, the access control to the resources is based on the one hand on mechanisms inherent in the principles of operation of the virtual memory, and on the other hand on a model of protection on 2 levels: supervisory mode (privileged, reserved more with the operation of the core) and the user mode (the least privileged). This type of access control is possible on the majority of the modern processors supporting an UNIX. Certain processors provide wider possibilities of protection. Thus the processors of the INTEL series ix86 comprise 4 levels (or rings) of protection. Operating systems (not very many at present), such as OS/2, exploit this possibility.

Sources of the article

Does certain passages of this article, or a previous version of this article, are based on the article Introduction to the systems UNIX of the Web site Comment it go? . The article of origin carries the following note of copyright: “© Copyright 2003 Jean-François Cotton flannel - Lodged by Web-solutions.fr. This document resulting from CommentCaMarche.net is presented to license GNU FDL. You can copy, to modify copies of this page as long as this note appears clearly. ”.

See too

Internal bonds

External bonds (in French)

  • ABC of UNIX (manual in free license GFDL)

  • Information on the administration system under UNIX
  • Graph of the evolution of the systems Unix
  • " fundamental of UNIX" : the famous French HOWTO presenting the operating process of the UNIX systems in general.

External bonds (in English)

  • Open Group holds mark UNIX® and the specifications of the system (rights transferred by Novell).
  • Page of Ritchie Refusals which gathers a certain number of documents on the history of UNIX.
  • Beautiful Labs, The Creation off the UNIX Operating System .
  • Twenty Years off Berkeley Unix (From AT&T-Owned to Freely Redistributable) , article of Marshall Kirk McKusick.
  • the 1 {{Re}} edition of the Handbook UNIX (1971).
  • UNIX History gives the graphic history of the operating systems Unix.
  • graphic complete, to print, on UNIX.

Beats-smg: UNIX Simple: UNIX Zh-min-nan: Unix Zh-yue: UNIX

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