If i'm not mistaken Dell computers come with Integrated Radeon 9800, not an actuall portable Radeon 9800...that means that it uses the system memory.
Having a portable GFX card has a great advantage because of much greater video memory B/W. Unified memory still requires a frame buffer. All digital graphics require the use of a frame buffer.
The frame buffer is where the information that is displayed on the screen is stored. The frame represents the screen and buffer means it's a chunk of reusable memory. The frame buffer is a chunk of memory to store what is displayed on the screen.
