Briefly the differences were these: modern to v7: remove all references to void no vi on v7, v6, and v5 so using ed instead. no conditional compilation so no way to make a truly universal version which works on everything. v7 to v6: use iolib instead of stdio: fopen -> copen, fclose -> cclose, fgetc -> cgetc, fputc -> cputc use int (no long or short in v6) call to srand uses different argument copen returns an int instead of a file pointer no strcat in v6 so the function had to be added v6 to v5: no iolib: fopen -> creat + open, copen -> open, cgetc -> read, cputc -> write, cclose -> close no scanf in v5 so I used the source for gets from v7 instead getchar() leaves a newline in the buffer so I added an extra call to getchar() immediately before each call to gets The size of the unirubik executable was 8K for modern Linux, 10K for v7, 10K for v6, and 5492 bytes for v5. Generally I was a lot slower trying to edit files with ed rather than vi but I'm a lot better with ed now. There wasn't really much unix v5 code to look at and I found the v5 manual a bit spartan. Mark