(03/02/2013 05:08 PM)Assassinator Wrote:  EDIT: I just realised it's an incredibly stupid comparison (in our case), the 8GB on the X720 is SYSTEM MEMORY, noone knows how much GRAPHICS MEMORY it has and what kind.  Why the hell are wee comparing system memory with graphics memory?  That's like saying my 2GB of memory on my GPU is faster than my 8GB of memory attached to my motherboard...

Details are fairly sketchy over how the memory works.  If they're using pure commodity parts, then there would be separate GPU and CPU memory, but it's feasible that a custom solution combines the two.
GDDR and DDR aren't that different, just the former typically operates at higher voltages and frequencies.