The evolution of the Unix operating system began with the Multiplexed Operating and Computing System (MULTICS) project in 1965. This was a joint project between Bell Laboratories, General Electric, and Massachusetts Institute of Technology.
However, MULTICS became too complex and Bell Laboratories withdrew its participation in the project in 1969.
One of the researchers in Bell Laboratories, Ken Thompson, started writing programs that simulated the behavior of the MULTICS file system. In 1969, he wrote the first version of Unix, called the Unixplexed Operating and Computing System (UNICS). The Unix programs were coded in assembly language.
In 1973, Thompson, along with Dennis Ritchie, who wrote the first C compiler, made a significant change to the Unix operating system with the fifth edition. The kernel, which was originally coded in assembly language, was rewritten in the C language.
The use of the portable C language also made Unix portable to different machines by recompiling the code for the specific target hardware platform.
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1. BSD-> While at the University of Berkeley, Thompson wrote the first Berkeley version of Unix with students Bill Joy and Chuck Haley. This version was distributed to students, who worked on the source code. The final version that incorporated all the modifications was named BSD, meaning Berkeley Software Distribution. From BSD came virtual memory, Sendmail, and support for TCP/IP. Some examples of Unix products based on BSD are: Sun OS 4.x (SUN), ULTRIX (DEC), NextStep (NeXT), LINUX.
2. System V-> Bell Laboratories felt that Unix was a commercially viable product and charged for it’s licensing fees. The System V operating system was developed by a consortium of vendor to an agreed standard, which incorporated many features to make it more powerful, reliable, and secure. For several years, System V was the most conservative, commercial, and well-supported strain of Unix products. The two most recent releases of System V, Release 3 (SVR 3.2) and Release 4 (SVR 4), remain popular. All System V products that are based on work carried out at Bell Laboratories require a license from the current owner, Unix System Laboratories. Some examples of System V products are: Sun OS 5.x/Solaris (SUN), HP – UX (HP), AIX(IBM), IRIX(SGI), Digital Unix (DEC), SCO UNIXware.
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Today, System V and BSD look very much alike. Then have a commonality of software, look and feel, and a broad set of features and commands.
Most versions of Unix have features of both System V and BSD, and users carry out tasks using BSD commands when that works best and System V commands at other times. Two of the main differences between the two versions are in the ways the ps and printing commands function.
The ps command reports the status of the current processes.
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