I ordered a 256MB ATI Radeon X1300 with my Dell computer and it is showing up as 128 MB, why is that?

This has happened twice I ordered a Dell computer with a 256MB ATI Radeon X1300 and the first time I got the computer it said 128 MN. I sent the computer back and the second time it said the same thing. So I searched about this and it says something about ATI's hypermemory cards and though it says 128 MB the card is borrowing memory from your computer therefore still making it a 256MB card. Does anyone have any information abut this?