can i put 3 gb of ram on my macbook it only has the stock 1 gb rite now but i'm wondering if i can just get 2gb and put it in the other slot? according to my macbook one of the slots is empty...

You need to check your exact specs here:

http://support.apple.com/specs/#macbook

but depending on your model, you can either put 2 or 4Gb in your machine.

yes,
to bottom line it more, i believe in these machines the ram chips must be installed in matched pairs.

as a proud owner of a MB core2duo…

…with 4 GB installed…

…with 3 GB recognized…

on a MB core2duo you can install :

- unmatched chips
- matched chips (then you benefit from interleaved memory, a slight boost)
- on all models have 4 GB installed, but on in the latest have them recognized as 4 GB, else you will have 3 GB at most (hardware limit), but the 4 recognized 3 work just fine (as I do)

for core duo owners, it's 2 GB, end of line.

See you specs here

r u saying that if i install 4GB it's only going to recognize 3GB? btw this is my computerand i'm looking to get the RAM for OWC(Other World Computing) or Samsung, are these reliable brands?

I have a MacBook Pro Intel Core Duo and it recognizes the 4GB 667 MHz DDR2 SDRAM. I got the Ram from Other World Computing and it's real slick! Hope this helps.

This macbook recognizes fully 4 GB.

Real Samsung is fine (as dane elec, MDT, gskill for example), OWC being a respectable mac centered dealer is fine too, in fact, I have OWC chips in my macbook
Don't mix macbook and macbook pro, they were not created equal, and the MBP recognized 4 GB from day one. It's a motherboard limitation on MB core duo max 2 GB, and same for MB core2duo 3 GB . In fact the left over 4th GB on early MB core2duo is so because it uses the same memory addresses as other ports on the motherboard like USB, SATA… there's nothing that can be done.

The biggest difference would be in video performance since the MB's use Intel integrated video that takes system RAM for video use.

The specific system in question uses an Intel GMA X3100 integrated "graphics processor with 144 MB of DDR2 SDRAM shared with main memory"

the general recommendation would be to use matched pairs for better video performance.

Note that on "3 GB" MB, the first few days with 4 GB in, you can have slight video bugs, but it disappears.