CPU usage doesn't add up with System Idle Process?

Question

I've always thought that 100% - System Idle Process = CPU Usage %. My task manager shows that my CPU is using 3% extra. For example, right now System Idle Process says 82, but CPU Usage is at 21%, instead of 18%. System Idle Process plus the other processes add up to 100, however. So what's up? Thanks.

The difference is 3%, consistently. Every time it refreshes. People I've asked have their CPU totaling 100. I'm afraid of something running in the background that i don't know about. =S

Answer 1

You have to remember that that task manager display is a snapshot in time.

While it is writing each line, the previous lines may have changed. By the time it is done, you are lucky the total is even close to 100%.