Wait until the applet below loads, then press the "Run Test" button. This will have your computer do 10 million operations, which takes Pentium machines anywhere from about 0.1 second up to about 1 second, depending on what else the machine is doing.

You can change the number of operations. For example, if you add another zero, making it 100 million operations, your machine should take about 10 times longer to complete them. This gives a better assessment of top speed.

The speed benchmark tells you something about how fast a given computer is, but does not really give you the whole picture in terms of that machine's capability to solve a certain class of problems.