I remember when I moved from netbeans to eclipse and the speed of compilation was amazing. For the uninitiated, Netbeans uses a traditional "compile and run" button, but Eclipse does incremental compilation as you type (and actually wrote its own Java compiler for this purpose, which almost exactly matches the Oracle compiler). You get real errors as you type, and when you press run the program instantly runs.

Didn't Donald Knuth or someone of that era write about this effect in Pascal IDEs?

(The best feature though is that you can run a program containing semantic errors or even minor syntax errors; the body of any function that doesn't compile gets compiled as a throw-exception statement, so you don't have to comment it out when you're working on another part of the code)