You need to make sure that your motherboard in your laptop can actually use 1gb of ram. Not all computers support 1gb, and some older machines (motherboards rather) might only support 512mb of ram. Just because it has 2 slots doesn't mean you can stuff a stick of 512mb in each....if it'll only recognize 512mb of ram and you put in 1gb, the computer will only use 512mb. Some mother boards will also only recognize certain sized modules (sticks of ram) and might not recognize a single 512 or 1gb stick.
Also, you'll have to check whether or not your motherboard uses sdram or ddram. The main difference (aside from speed) is that ddram (Double Data ram) runs faster in pairs, while sdram (Single Data ram) doesn't matter if it's a single stick or a pair or 57 sticks or ram, it's still single data.
You can use SIW
(System Information for Windows) to figure all this out. Click on "Motherboard" to see the details of your motherboard, paying special attention to the "Memory summary" section.
Hope this helps!
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