Asus GTX 570 4048MB?

-XTC-

Honorable
Jun 22, 2013
46
0
10,530
Alright, so I bought this dirt-cheap PC today and decided that I was going to upgrade the GPU so I have myself a decent rig at a decent price. These are the specs;

Intel Core i5-4670K @ 3.4 GHz
16GB Corsair RAM
Asus GTX 570 (4GB?)
Corsair H80i liquid cooling
128GB OCZ SSD
1TB WD HDD
Cooler Master Silencio 352 Case
24" AOC 1920x1080p display

All for £350 which in my opinion is a bargain. But there lays the question. I'm not great with GPU's and stuff but for some reason, I still can't get my head around why the 'dxdiag' is reading the GPU as being 4GB? I don't know if I'm taking in this information wrong but as far as I'm aware, the GPU only came at a 2GB max so unsure of what's going on. Is there some other way to find out how much power the GPU really has?