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Dated: Aug. 13, 2004
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UnixTo understand why the UNIX operating system has so many commands and why it’s not only the premier multiuser, multitasking operating system, but also the most successful and the most powerful multichoice system for computers, you’ll have to travel back in time. You’ll need to learn where UNIX was designed, what were the goals of the original programmers,and what has happened to UNIX in the subsequent decades.
Unlike DOS, Windows, OS/2, the Macintosh, VMS, MVS, and just about any other operating system, UNIX was designed by a couple of programmers as a fun project, and it evolved through the efforts of hundreds of programmers, each of whom was exploring his other own ideas of particular aspects of OS design and user interaction. In this regard, UNIX is not like other operating systems, needless to say!
It all started back in the late 1960s in a dark and stormy laboratory deep in the recesses of theAmerican Telephone and Telegraph (AT&T) corporate facility in New Jersey. Working withthe Massachusetts Institute of Technology, AT&T Bell Labs was codeveloping a massive,monolithic operating system called Multics. On the Bell Labs team were Ken Thompson,Dennis Ritchie, Brian Kernighan, and other people in the Computer Science ResearchGroup who would prove to be key contributors to the new UNIX operating system.
When 1969 rolled around, Bell Labs was becoming increasingly disillusioned with Multics,an overly slow and expensive system that ran on General Electric mainframe computers thatthemselves were expensive to run and rapidly becoming obsolete. The problem was thatThompson and the group really liked the capabilities Multics offered, particularly theindividual-user environment and multiple-user aspects.
In that same year, Thompson wrote a computer game called Space Travel, first on Multics,then on the GECOS (GE computer operating system). The game was a simulation of themovement of the major bodies of the Solar System, with the player guiding a ship, observingthe scenery, and attempting to land on the various planets and moons. The game wasn’t muchfun on the GE computer, however, because performance was jerky and irregular, and, moreimportantly, it cost almost $100 in computing time for each game.
In his quest to improve the game, Thompson found a little-used Digital EquipmentCorporation PDP-7, and with some help from Ritchie, he rewrote the game for thePDP-7. Development was done on the GE mainframe and hand-carried to the PDP-7 onpaper tape.
Once he’d explored some of the capabilities of the PDP-7, Thompson couldn’t resistbuilding on the game, starting with an implementation of an earlier file system he’d designed,then adding processes, simple file utilities (cp, mv), and a command interpreter that he calleda "shell.” It wasn’t until the following year that the newly created system acquired its name,UNIX, which Brian Kernighan suggested as a pun on Multics.
The Thompson file system was built around the low-level concept of i-nodes—linked blocksof information that together comprise the contents of a file or program—kept in a big listcalled the i-list, subdirectories, and special types of files that described devices and acted asthe actual device driver for user interaction. What was missing in this earliest form of UNIXwas pathnames. No slash (/) was present, and subdirectories were referenced through aconfusing combination of file links that proved too complex, causing users to stop usingsubdirectories. Another limitation in this early version was that directories couldn’t be addedwhile the system was running and had to be added to the preload configuration.
In 1970, Thompson’s group requested and received a Digital PDP-11 system for the purposeof creating a system for editing and formatting text. It was such an early unit that the first diskdid not arrive at Bell Labs until four months after the CPU showed up. The first importantprogram on UNIX was the text-formatting program roff, which—keep with me now—wasinspired by McIlroy’s BCPL program on Multics, which in turn had been inspired by anearlier program called runoff on the CTSS operating system.
The initial customer was the Patent Department inside the Labs, a group that needed a systemfor preparing patent applications. There, UNIX was a dramatic success, and it didn’t takelong for others inside Bell Labs to begin clamoring for their own UNIX computer systems.
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