A mechanism is provided for approximating data switching activity in a data processing system. A data switching activity identification mechanism in the data processing system receives an identification of a set of data storage devices and a set of bits in the set of data storage devices in the data processing system to be monitored for the data switching activity. The data switching activity identification mechanism sums a count of the identified bits that have changed state for the data storage device along with other counts of the identified bits that have changed state for other data storage devices in the set of data storage devices to form an approximation of data switching activity. A power manager in the data processing system then adjusts a set of operational parameters associated with the data processing system using the approximation of data switching activity.