Apropos of file types, which Rich Salz commends Unix for discarding. Early in Multics development, I and others visited various influential time-sharing systems in search of good ideas. I tried each one on a simple model of software updating, in particular of remaking a compiler. In every instance I could not make my program work without expert help to get past file-type barriers. My model was based on a trivial Fortran program that copied input to output until an input line with END in column 7 had been processed. Every system was able to compile this program, but ... After compiling, I tried to use the program to make a copy of itself. Here was the first file-type hurdle. Input was typically expected to be of type data, not source code. Gurus had to scramble to overcome this nominal incompatibility. Next I tried to compile the new Fortran program. Same trouble in reverse--data used as source. More scrambling of gurus. Then I ran the newly compiled program to do the above steps over again. This time the gurus had the file-type workarounds under control. One comp center still had trouble, however, which took some time to diagnose. It turned out that Fortran programs were, for unknown reasons, specifically forbidden to read their own source code! One side effect of file-type conventions was that instead of learning once and for all how to create text files, one had to learn different ways to edit files of different types. Doug