How does the memory work on the PS4 and Xbox One?

For PCs, the memory is referred to as either DDR1, DDR2, DDR3, DDR4. The Xbox One and PS4 but this is the 8 GB GDDR5 RAM, I'm confused because GDDR5 RAM is not a VRam type?

GDDR is actually for graphics cards. Since it would not be worthwhile to build 2x RAM, you just build GDDR and use it for the CPU as well.

GDDR is more expensive, but as I said, double RAM would be even more expensive.