How to determine which RAM will be compatible with system

I run windows XP on COmpaq presario and want to increase the amount of RAM I have available. I am currently running 128 Mbs and would like to increase to at least 512Mbs. 1Gb would be favorable. How do I know if RAM I find is compatible with my system? I am assuming that I do not have to order it from Compaq only. Any help appreciated.

Thanks!

 

Here is a memory configurator , should tell you what memory you need granted you do not have to use this brand of memory it will tell you what speed ram you need.

Patriotmem.com - Configurator

 

Depending on the model, if it is an older Compaq Presario, the most it may take is 512mb. Crucial, or memory.com has Memory configurators, along with the information on Compaq.com for the system will tell you.

 

As has been said depending on the age of the computer and whether its a desktop or laptop you will most likely need 2 sticks of 256mb pc100,its easier to dump your 128mb stick and put 2 new ones in there

I'm suprised youy can stand running xp with only 128mb of memory it really needs 256 or 512

 

I cannot stand using XP with this minimal amount of memory. Unfortunately, I cannot stand the thought of back sliding to another operating system either. Thanks for all of the information!!!