My first job working in IT was as a Helpdesk officer for a university. Back in those days, computers were only just starting to become common place in education and business. I happened to have a few old components floating around that were past their useful date, and decided to create a Demo PC for students to look at and show them the inarts of the mysterious computer.
I used an old rolling table, fitted a plywood board on a 60 degree angle, and screwed a mother board onto it. I also fitted a 5.25" diskdrive and a (I think) 5 MB MFM harddisk (yeah I know, it was a while back...) with the cover removed and a bit of perspex on top. I fitted and connected a monitor (we had color monitors back in those days, this one was green :-P), wrote a little Turbo Pascal program that would move the heads of the hard disk, and display on the monitor text stating so, and then move the diskdrive heads.
Main components such as CPU, memory bus and so on where labelled. With the Demo PC on wheels it could easily be rolled into class where teachers would use it. Plug it into the wall and it would start working.