I was surprised when I heard that Pascal didn't originally have units. If I recall correctly they were introduced in Turbo Pascal 4. Did other pascal version have units prior to that? How long before other Pascal's got units? 
Was in it Turbo Pascal 4 that Unit were introduced?
history;pascal
The Pascal programming language didn't have any modularity construct. Early versions of Turbo Pascal didn't have them either.  Turbo Pascal 3 consisted of about 40kB of code (including the editor); there wasn't any room for advanced language features. Units were introduced in Turbo Pascal 4.0. The concept was certainly not new (Modula-2, a successor of Pascal, had a similar primitive module system at the time, and so had other languages before), and the term compilation unit was also already in common use.