RAM not all showing up

hello i bought a used computer from petrocanada and it has 2 4 gig sticks in it. i had to put windows on and i checked my system it only shows up 2.50 i dont know how to fix plz help and hurry it is a sun mirco system computer
 
What operating system do you have? If I remember correctly, the fist version of XP will only read 3.33 gigs of ram, no matter how much you have in it.
 
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