Back before the personal computer age, computers had lights and toggle switches. One could use the switches to program computers and read answers in the lights. All in binary of course. We also used these tools for debugging. One could enter a memory address using the switches and see what was in the location, data or instruction, in the lights.
If a computer program was hung in a loop one could halt the computer and see what address and instruction was part of the loop. It was a useful debugging tool. Similarly if the computer halted for some reason an error code might be displayed in lights.
It wasn’t all seriousness though. Many operating systems would display something in the lights when the computer was idle – not doing real work. Usually this was some sort of animation – lights racing though the strip and rows of lights. Digital Equipment Corporation had a computer type called the PDP-11 that supported a number of different operating systems. Each OS had it’s own idle loop light display. One could walk into a computer lab, typically at night when no one was using the computers, and tell which OS was running on which computer just by watching the lights.
Some manifaxine computers had a lit of lights. A company called Burroughs had one large computer that would display the company logo in the lights when it was idle. Now you never really want to see that display if you owned that computer. It was frightfully expensive to buy and operate so you really wanted it to be doing real work 24/7. One potential buyer wanted their company logo to display when the computer was idle. Vanity perhaps? Anyway, silly as it was, as I recall, the program change was made and the sale went though.
Today, those sorts of lights are an unwanted, and generally unneeded, expense. I do sometimes miss those simpler days though.
