I recall that when I was around my 16 to 19 years old I was completely amazed by the possibility of running a different operating system inside a window on my system. At the time I was using a Commodore Amiga, and I had software to emulate Atari, Apple and MS-Dos systems. The first two used the same CPU as my native system, and the later was a complete emulation off an Intel x86 CPU. Because of this, performance was really awful, but nevertheless it was very interesting to use.