there are many ways to find that information
you can use the serial number of your mac (find it in "about this mac or on a sticker in the battery compartment - put the serial number in the green serch field on [http://appleserialnumberinfo.com/Desktop/index.php|appleserialnumberinfo.com] and you get all the informations you "never" wanted to know about your mac ;-)
[http://support.apple.com/kb/ht1635|How to identify MacBook models]
(the colored text's are links ;-) )