What is important here is not the Ram amount on your system, but the video memory present on your graphic card.
And according to Shawn, displacement is on on many materials (hadn't seen this myself), and memory reqirement for displacement can be quite high, both graphic and system ram. There is an amount limit for for displacment display and ecosystem display in the display options box. This is the max amount Vue will use. You can either lower or up this value according to your graphic card's memory amount, with a limit at 1 gig.