cpuinfo is a virtual file located in the /proc filesystem. When accessed, it provides real-time information both about unchanging hardware characteristics of the CPU, and about how it is currently running (most notably, what clock speed it or each of its cores is at).
I just installed screenlets to get some onscreen information about my system. I'm trying the RingSensors screenlet to monitor cpu load, but there are more sensors available to monitor than I'd expect. ...