4.1. Approaches to Measuring
Making measurements involves gathering data and processing it so that it is usable. There are several common approaches to acquiring data to measure activity in a computer system. They fall into three groups:
External hardware monitors
Internal hardware monitors
Internal software monitors
4.1.1. External Hardware Monitors
External hardware monitors usually involve probes, such as printed circuit boards which plug into the computer backplane or attach directly to the integrated circuits on the CPU board itself. These hardware monitors are triggered by events such as instruction execution or hardware interrupts. The accumulation of data typically occurs so rapidly that some external storage mechanism is required to save ...