Way back in 1982 or so, I built my first computer. I was thirteen years old and it comprised a Z80 processor, a few logic circuits, some switches for input and a handful of red LED displays for output. I built it with a friend and our mathematics teacher during the school lunch breaks and after a few weeks of dodgy soldering we finally completed a machine that could add and subtract a few binary numbers. It was considerably less powerful than the pocket calculators we had even in those days, but we'd learned a lot building it and had a lot of fun.