Some embodiments of the invention provide a system for tracking utilization of resources of computers. This system includes several client computers, where each computer has one or more resources that the system tracks. The system also includes a client application for each client computer. Each client application collects utilization duration data relating to the utilization of the resources of its corresponding client computer. The system further includes an application server that receives the utilization duration data collected by the client applications and stores the received data in a storage structure. In certain embodiments, the collected duration data includes time periods that the client applications measure. The application server then aggregates and/or stores the collected time periods. One of ordinary skill will realize that in other embodiments the client applications might report raw duration data (such as start and end times) from which the application server generates the appropriate time periods.