windows xp blinking light

wha can you tell me about the little red led light on my pc that blinks on and off. Someone told me that you can tell what th pc is doing by watching this light. I surmised that if it is blinking, that it is searching the hard drive for something. Does it go off or stay on steady when it is done searching. ?? Are there any other indications ??

 

Sounds like the hard drive activity light.
Anytime the computer accesses data on the hard drive
the light will flash.
During times of high activity,it may look like it is on constantly.
During low activity,it flashes periodically.