Most computers have a "CPU busy light" with a sillo icon beside it that lights up periodically. But what exactly does that light mean? Is it turned on when the CPU is in Usage or when the hard drive I/O is up? I noticed more of a correlation with the disk I/O then the CPU usage.
The silo light should indicate disk I/O, not CPU activity. It means that your disk is being accessed (read from or written to).
While I actually HAVE seen a CPU activity indicator, it was way back in the 90s using an add-on card that showed part of the address the CPU was accessing, and the card was located inside the computer.