PL/1, RPG, COBOL, FORTRAN, DBASE II, Basic in various flavours, Z80 Assembler, 6502 Assembler, 68000 Assembler, 80×86 Assembler. Forth, C, C++, Visual Basic, Visual C++, Java, Ruby, and now Objective C. There are others that I can’t remember the name of.

That’s about 18 or more. It’s the way things go, the profession has fast moving technology. Things continually change. I could add in the dozens of architectures and hardware specifics I have worked with too.

The consequence is that you are continually learning, you never get mastery of everything you need, as in other professions. Even medicine has changing technology, but I think, software development is maybe a leader on requiring constant retraining and education for its professionals on such a scale.