Keyboard lights were pretty useful for debuging back in Turbo Pascal days. XT had only 640K memory. Borland managed to fit IDE into this memory with code assi

Keyboard lights were pretty useful for debuging back in Turbo Pascal days. XT had only 640K memory. Borland managed to fit IDE into this memory with code assistant and interactive debugger. But if your program consumed too much memory, IDE would not fit and you had to use other means for debugging; there was speaker, printer and keyboard lights.