Far from the bright lights of the ARPANET, off in the wilds of New Jersey, something else had been going on since 1969 that would eventually overshadow the PDP-10 tradition. The year of ARPANET's birth was also the year that a Bell Labs hacker named Ken Thompson invented Unix.
Thompson had been involved with the development work on a time-sharing OS called Multics, which shared common ancestry with ITS. Multics was a test-bed for some important ideas about how the complexity of an operating system could be hidden inside it, invisible to the user, and even to most programmers. The idea was to make using Multics from the outside (and programming for it!) much simpler, so that more real work could get done.
Bell Labs pulled out of the project when Multics displayed signs of bloating into an unusable white elephant (the system was later marketed commercially by Honeywell but never became a success). Ken Thompson missed the Multics environment, and began to play at implementing a mixture of its ideas and some of his own on a scavenged DEC PDP-7.
Another hacker named Dennis Ritchie invented a new language called `C' for use under Thompson's embryonic Unix. Like Unix, C was designed to be pleasant, unconstraining, and flexible. Interest in these tools spread at Bell Labs, and they got a boost in 1971 when Thompson & Ritchie won a bid to produce what we'd now call an office-automation system for internal use there. But Thompson & Ritchie had their eye on a bigger prize.
Traditionally, operating systems had been written in tight assembler to extract the absolute highest efficiency possible out of their host machines. Thompson and Ritchie were among the first to realize that hardware and compiler technology had become good enough that an entire operating system could be written in C, and by 1978 the whole environment had been successfully ported to several machines of different types.
This had never been done before, and the implications were enormous. If Unix could present the same face, the same capabilities, on machines of many different types, it could serve as a common software environment for all of them. No longer would users have to pay for complete new designs of software every time a machine went obsolete. Hackers could carry around software toolkits between different machines, rather than having to re-invent the equivalents of fire and the wheel every time.
Besides portability, Unix and C had some other important strengths. Both were constructed from a ``Keep It Simple, Stupid'' philosophy. A programmer could easily hold the entire logical structure of C in his head (unlike most other languages before or since) rather than needing to refer constantly to manuals; and Unix was structured as a flexible toolkit of simple programs designed to combine with each other in useful ways.
The combination proved to be adaptable to a very wide range of computing tasks, including many completely unanticipated by the designers. It spread very rapidly within AT&T, in spite of the lack of any formal support program for it. By 1980 it had spread to a large number of university and research computing sites, and thousands of hackers considered it home.
The workhorse machines of the early Unix culture were the PDP-11 and its descendant, the VAX. But because of Unix's portability, it ran essentially unaltered on a wider range of machines than one could find on the entire ARPANET. And nobody used assembler; C programs were readily portable among all these machines.
Unix even had its own networking, of sorts -- UUCP: low-speed and unreliable, but cheap. Any two Unix machines could exchange point-to-point electronic mail over ordinary phone lines; this capability was built into the system, not an optional extra. In 1980 the first USENET sites began exchanging broadcast news, forming a gigantic distributed bulletin board that would quickly grow bigger than ARPANET. Unix sites began to form a network nation of their own around USENET.
A few Unix sites were on the ARPANET themselves. The PDP-10 and Unix/USENET cultures began to meet and mingle at the edges, but they didn't mix very well at first. The PDP-10 hackers tended to consider the Unix crowd a bunch of upstarts, using tools that looked ridiculously primitive when set against the baroque, lovely complexities of LISP and ITS. ``Stone knives and bearskins!'' they muttered.
And there was yet a third current flowing. The first personal computer had been marketed in 1975; Apple was founded in 1977, and advances came with almost unbelievable rapidity in the years that followed. The potential of microcomputers was clear, and attracted yet another generation of bright young hackers. Their language was BASIC, so primitive that PDP-10 partisans and Unix aficionados both considered it beneath contempt.