One of the interesting things that the Unix Heritage Society does is that it lets us go back and see just what a remarkable thing Seventh Edition Unix was, how much it was an aesthetic flowering and really created a lot of what we now think of as 'Unix'.

It does this not so much by letting us going back to see V7 as it was (by modern standards, V7 is nothing terribly impressive and is in some ways rather primitive). Rather, it does this by letting us go back and see the Sixth Edition (V6) as well as V7. Looking at both versions makes it very clear just how much of a jump there was between V6 and V7, and thus how much of what we think of as 'the Unix way' only appeared in V7 and was not a straightforward evolution from V6.

My impression is that this flowering was not so much from the low level details of the system (the V6 and V7 system call lists are pretty similar, for example), but from higher level programs and decisions. Many of what we think of as signature Unix programs only appeared in V7, things like awk , make , even sed . (And the Bourne shell .)

Sidebar: the V6 shell

The V6 shell is (or seems to be) by modern standards a rather peculiar beast. I particularly enjoy how commands like exit and its looping construct were implemented: rather than being builtins, they used seek() to change the position of the shell's command file descriptor, so that the shell would read a different next command. (Or in the case of exit , so that the shell would immediately see end-of-file.)