Processor Issue

I have an older Dell laptop with a 1.6Ghz pentium processor and 512 mb of RAM. I

I recently noticed that when I click Properties on MyComputer sometimes it show:

1.60 GHz, 512 MB of RAM

----

and other times it shows: 591 MHz, 512 MB of RAM.

Does anyone have an idea of what is happening?

Thanks for your help.

Are you using a battery when it's running at the slower speed?

That's about all I can think of so maybe rridgely knows since his uses laptops allot.

I always use the AC Adapter, never batteries.

I think I figured it out--this is the Intel Speed Step Technology working.