The first step you should use to measure the effect of an application on a computer configuration is to determine how the computer responds to different levels of application activity.
The most common indicator of the activity of an application that generates dynamic pages is rate of requests to the application. CGI and ISAPI applications become active when they respond to requests and are generally inactive between requests. The more requests the application responds to, the more active it is judged to be.
First, you measure the activity level of an application. Then you can compare the effect of different levels of activity of a single application on the computer. You can also compare the effect of the same activity levels of different applications.