Windows XP users - M1530 battery/charger question

To all XP users (32-bit/x64), what is controlling the brightness of your screen when you unplug the A/C adapter from the M1530? Is it Dell's system board or is it a Windows program?

Reason why I'm asking is because my screen is at brightest when plugged in, and dim when it's unplugged. But if the A/C adapter is unplugged and I brighten the screen using Fn+Up keys, and then plug it back in and then out, it becomes bright still. Normally, on my previous Windows Vista installation, it gets reset to default configuration: brightest when plugged in, dim when unplugged. Sorry for the long explanation, but I hope it's clear. Any ideas?

 

Its the windows oporating system and the motherboard.

 

Yes its both. The BIOS has an option where you can change the brightness when your A/C is unplugged and when its plugged in.
I think that windows XP keeps the screen bright because you gave the orders by using FN+UP so XP uses that one.

 

I'm using Dell Quickset that I downloaded from Inspiron 1520 w/XP link. Works great for creating profiles say for brightness on battery.

http://support.dell.com/support/down...&fileid=246458