Friday, 16 September 2011

UNIX: A bit of history

UNIX started back in 1969 in BTL(Bell Telephone Labs) and AT&T.These were just withdrawn from a project called MULTICS,which was designed to create an OS to support thousands of users simultaneously.BTL,General Electric,MIT were involved in this project,as it failed MIT was withdrawn from the project

Two engineers who were involved in MULTICS were Ken Thompson and Dennis Ritchie, found a computer which had an assembler and loading program.They developed tests on these assembler with the kernel.
Ken Thompson(Left) and Dennis Ritchie

1969, Thompson had an idea of writing a file system for the created kernel so that files are stored in an ordered form in a hierarchical way. As progress made on the system design few more BTL engineers joined the project. The system became too small to work on and to purchase PDP machine with an agreement of creating a new text processor.

when new machine arrived they gave only CPU and memory not disk or OS.Thompson unable to wait designed a RAM disk in memory and used half of memory as disk other half for OS that he was designing. Once the disk arrived they stared working on OS and promised text processor(Troff)which was used to create UNIX "man pages". BTL started using UNIX with new text processor.

Another important characteristic was that UNIX was independent of hardware architecture. 1971, external users wanted to document what was being done resulted in UNIX programmers manual signed by Thompson and Dennis. UNIX installations continued to grow to about 50

End 1973,decision to present results at a conference on OS, so various IT  centers, universities asked for copies of UNIX. AT&T did not support, so users had to unite and share their knowledge by forming community(USENIX). AT&T decided to cede UNIX to universities,but no support.

University to obtain license was Berkley where Thompson studied.1975 Thompson returned to Berkley as a teacher bringing with him the latest kernel.Two newly graduated students, Chuck Haley and Bill Joy joined him and started to work together in UNIX implementation.

Bill Joy

The major disappoinment were the editors, Joy perfected an editor called "EX" later the same into "vi".Two developed Pascal language compiler which was added into UNIX.Demand continued to grow for UNIX which made Joy to produce "BSD UNIX"

1978, BSD had a license regarding its price for distribution so that new users could end making some changes or incorporating features,selling copies after certain period of time.

Joy made further changes to "vi" in such a way that editor was independent of terminal. He created the TERMCAP system programs could get executed irrespective of the terminals using interface. 1977, UNIX was running on PDP machines, that year adaptations were made for machines of the time such as Interdata and IBM.More versions offered as it included:awk,lint,make,uucp,C compiler designed by Kernighan and Dennis Ritchie which had created to re-write most UNIX that was initially running in assembler.Also included with bash,find,cpio,expr

UNIX started to appear from companies such as Xenix,Berkely. AT&T realised that UNIX was only a commercial product and its license prohibited its study in academic institutions in order to protect its commercial secret. until then UNIX source code was used in universities to teach OS

Every one found their own solution for solving problems.Andrew Tanenbaum decided to write a new UNIX-compactable OS without using a sinlge line of AT&T code.He called this OS as MINIX.

Bill Joy decided to leave to a new company called SUN Microsystems where he modified the BSD 4.2 to newly created SUN's UNIX (SunOS). Every company stared using their own UNIX.

- IBM     - AIX
- DEC     - Ultrix
- HP      - HPUX
- SGI     - IRIX
- Apple   - MacOS X

AT&T released final version called UNIX System V(SV),as well as BSD 4.x.Current UNIX versions are either running on SV or BSD.some manufactures specify their UNIX in BSD or SV style.Later which UNIX standards were drawn up hence we find IEEE POSIX, UNIX 97, FHS .. etc