Released on 20 November 1987, Version 4 was a total rewrite, with both look and feel and internal operation much changed. The compiler generated executables in .EXE format under DOS, rather than the simpler but more restricted .COM executables. The by-then-obsolete CP/M and CP/M-86 operating system versions were dropped when TP was rewritten. Version 4 introduced units, and a full-screen text user interface with pull-down menus; earlier versions had a text-based menu screen and a separate full-screen editor. (Microsoft Windows was still very experimental when the first version was released, and even mice were rare.)