It was a free version of Unix with complete source code.

Further, each vendor's version of Unix was different to some degree.

In early versions of Unix the history command was a separate program.

These companies provide many different versions of Unix, limiting the system's appeal.

This is very important, because the original versions of Unix did not have any copyright claim in the source code.

Both machines ran a version of Unix modified for parallel computing.

V7 was the first readily portable version of Unix.

Within two years the foundation plans to release a competing version of Unix that will be available on many hardware brands.

Mike's paid his dues on ancient versions of Unix, dating back to the '70s.

This syntax was already present by the release of the first version of Unix in 1971.