A Brief History of UNIX
To 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 the goals of the original programmers were, 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 or her 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 the American Telephone and Telegraph (AT&T) corporate facility in New Jersey. Working with the Massachusetts Institute of Technology, AT&T Bell Labs was co-developing 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 Research Group 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 that themselves were expensive to run and rapidly becoming obsolete. The problem was that Thompson and the group really liked the capabilities Multics offered, particularly the individual-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 the movement of the major bodies of the solar system, with the player guiding a ship, observing the scenery, and attempting to land on the various planets and moons. The game wasn't much fun on the GE computer, however, because performance was jerky and irregular, and, more importantly, it cost almost $100 in computing time for each game.
In his quest to improve the game, Thompson found a little-used Digital Equipment Corporation PDP-7, and with some help from Ritchie, he rewrote the game for the PDP-7. Development was done on the GE mainframe and hand-carried to the PDP-7 on paper tape.
Once he'd explored some of the capabilities of the PDP-7, Thompson couldn't resist building on the game, starting with an implementation of an earlier file system he'd designed, and then adding processes, simple file utilities (cp, mv), and a command interpreter that he called a “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 blocks of information that together compose the contents of a file or program—kept in a big list called the i-list, subdirectories, and special types of files that described devices and acted as the actual device driver for user interaction. What was missing in this earliest form of UNIX was pathnames. No slash (/) was present, and subdirectories were referenced through a confusing combination of file links that proved too complex, causing users to stop using subdirectories. Another limitation in this early version was that directories couldn't be added while 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 purpose of creating a system for editing and formatting text. It was such an early unit that the first disk did not arrive at Bell Labs until four months after the CPU showed up. The first important program on UNIX was the text-formatting program roff, which—keep with me now—was inspired by McIlroy's BCPL program on Multics, which in turn had been inspired by an earlier program called runoff on the CTSS operating system.
The initial customer was the Patent Department inside the Labs, a group that needed a system for preparing patent applications. There, UNIX was a dramatic success, and it didn't take long for others inside Bell Labs to begin clamoring for their own UNIX computer systems.
The C Programming Language
That's where UNIX came from. What about C, the programming language that is integral to the system?
In 1969, the original UNIX had a very-low-level assembly language compiler available for writing programs; all the PDP-7 work was done in this primitive language. Just before the PDP-11 arrived, McIlroy ported a language called TMG to the PDP-7, which Thompson then tried to use to write a FORTRAN compiler. That didn't work, and instead he produced a language called B. Two years later, in 1971, Ritchie created the first version of a new programming language based on B, a language he called C. By 1973, the entire UNIX system had been rewritten in C for portability and speed.
UNIX Becomes Popular
In the 1970s, AT&T hadn't yet been split up into the many regional operating companies known today, and the company was prohibited from selling the new UNIX system. Hoping for the best, Bell Labs distributed UNIX to colleges and universities for a nominal charge. These institutions also were happily buying the inexpensive and powerful PDP-11 computer systems—a perfect match. Before long, UNIX was the research and software-development operating system of choice.
The UNIX of today is not, however, the product of a couple of inspired programmers at Bell Labs. Many other organizations and institutions contributed significant additions to the system as it evolved from its early beginnings and grew into the monster it is today. Most important were the C shell, TCP/IP networking, vi editor, Berkeley Fast File System, and sendmail electronic-mail-routing software from the Computer Science Research Group of the University of California at Berkeley. Also important were the early versions of UUCP and Usenet from the University of Maryland, University of Delaware, and from Duke University. After dropping Multics development completely, MIT didn't come into the UNIX picture until the early 1980s, when it developed the X Window System as part of its successful Athena project. Ten years and four releases later, X is the predominant windowing system standard on all UNIX systems, and it is the basis of Motif, OpenWindows, and Open Desktop.
Gradually, big corporations have become directly involved with the evolutionary process, notably Hewlett-Packard, Sun Microsystems, and Digital Equipment Corporation. Little companies have started to get into the action, too, with UNIX available from Apple for the Macintosh and from IBM for PCs, RISC-based workstations, and new PowerPC computers.
Today, UNIX runs on all sizes of computers, from humble PC laptops, to powerful desktop-visualization workstations, and even to supercomputers that require special cooling fluids to prevent them from burning up while working. It's a long way from Space Travel, a game that, ironically, isn't part of UNIX anymore.