This is 1GB RAM times 2 modules, so a total of 2GB of RAM from my 2009 MacBook that I recently upgraded to 4GB of RAM (aka memory modules). I reloaded the pics. Listia or my iPhone was acting a little psycho last night, sorry.
They will only work in a MacBook/MacBook Pro. We upgraded the RAM on my husband's iMac (desktop) and they are different as far as the location of the placement notch.