The best BYTE for me was the one where they published the entire source code of a Pascal compiler, written in Basic. Up till then I was completely mystified how a compiler worked. In figuring out every line of that compiler, I felt like somebody turned the lights on.

Later on, I was using a Pascal compiler on the PDP-11. I'd write bits of code, compile them, and look at the assembler. I was especially impressed with the clever way nested functions worked (the static link pointer). Nested functions in D are implemented the same way :-)