You can't demo any PC without demonstrating software, otherwise there would be no point even switching it on.
Even the basic Windows desktop screen doing nothing is still running software. Moving the mouse uses software, and pressing a key and seeing a letter appear on a screen uses software.
So it is legitimate to demo photo-processing software (for example) as a way of showing how fast the computer responds. Having lots of windows open doing different things also demontrates this.
The PC I am using now is so slow that when I move the mouse, there is a delay before the cursor moves. And sometimes I look up after typing a sentence to see only a few letters there, then the rest of them appear as if by magic.
Perhaps I could sell it to QVC (for a lot of money) so they can compare it to the latest PC they are flogging.