Interface

• Each ATI Radeon HD 2400 and AMD Radeon HD 6990 card is installed on a desktop computer using the Peripheral Component Interface Express (PCI-E) expansion slot on the motherboard. This is made possible by the 16-lane (x16) interface each GPU possesses. The card installed on the Dell XPS One, though, uses v1.0, or PCI-E 1.0 x16, which means that it has a data transfer speed of 4GB per second. The Radeon HD 6990 uses the PCI-E 2.1 x16 standard, which doubles the data transfer rate to 8GB/s.
  
  

Memory

• The ATI Radeon HD 2400 graphics card shares 256MB of the Dell XPS One's 2MB of random-access memory (RAM). The GPU uses such memory for the computer's video and graphics capabilities. The AMD Radeon HD 6990, on the other hand, has its own memory, meaning that rather than borrow RAM from the XPS One, it uses the memory built into it. Also, it offers 4GB, which is 16 times as much as the memory that the Radeon HD 2400 uses.
  
  

Display and Connectors

• For hooking up the Dell XPS One's monitor, the ATI Radeon HD 2400 offers two connectors: Video Graphics Array (VGA) port for analog display and Digital Visual Interface (DVI) for digital display. The VGA and DVI connectors support up to a maximum resolution of 2,048 by 1,536 pixels and 2,560 by 1,600 pixels, respectively. The AMD Radeon HD 6990 omits the VGA port. However, it has a connector missing on its predecessor: a DisplayPort for transmitting digital audio/video content and supporting the same maximum resolution as the VGA. Complementing the DisplayPort and offered on both GPUs is the High-Definition Multimedia Interface (HDMI). The standard connector for high-definition televisions (HDTVs), the HDMI output supports up to 1,920 by 1,080 pixels in resolution.
  
  

Fill Rate

• Each graphics card has a fill rate, which is the number of pixels that it uses for a computer screen display per second. The ATI Radeon HD 2400 has a fill rate of 2,100,000,000 pixels per second. The AMD Radeon HD 6990, however, greatly outperforms its predecessor with a fill rate of 53,120,000,000 pixels per second.