[NAME] If you look at the Service Manual diagram (on page 12)  of the motherboard you will see the location of the 4 RAM slots.  
Hello Dell,      I have purchased DELL XPS 8900 desktop. According from the specification it should have 4 slots of RAMs. However, today I opened it and only can see 2 RAMs slots not 4.  Can you please let know why my Dell machine only come with 2? I have trouble to contact Dell Support team. So I hope you can answer my answer. Thanks Loi Vuong 
XPS 8930 - How many slots of RAM, 2 or 4?