A long time ago (1969), Unix said "papa" for the first time at AT&T (then called Bell Laboratories, or Ma Bell for the intimate) on a PDP-7. Everyone liked Unix very much and its widespread use we see today is probably due to the relative simplicity of its design and of its implementation. (It is written, of course, mostly in C.)
However, these facts also contributed to everyone developing their own dialect. In particular, the University of Berkeley at California distribute the so-called BSD (8) Unix whereas AT&T now distribute (sell) System V Unix. All other versions of Unix are descendants of one of these major dialects.
The differences between these two major flavors should not upset most application programs. In fact, we would even say that most differences are just annoying.
BSD Unix has an enhanced signal handling capability and implements sockets. However, all Unix flavors differ significantly in their raw I/O interface (that is, the ioctl system call), and this should be avoided if possible.
The reader interested in knowing more about the past and future of Unix can consult "A Single Standard Emerges from the UNIX Tug-Of-War" [11] and "Interview With Five Technologists" [6].
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The Language
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