trying to get my Dell xps 400 to recognize faster memory; bios still shows 667mghz, need it to show 800

Dell has 800m Mhz as an option for this model; as an upgrade.  

You've searched for Dimension XPS Generation 4,

accessories.us.dell.com/.../category.aspx

Hi fredamristead,

Dimension XPS 400 supports two channels of four sockets of 400 MHz, 533 MHz, and 667 MHz DDR2 memory. Hence, 800 MHz memory speed is not compatible with your system.

Please reply for any further questions.

The Dell rep is correct; the XPS 400 has a memory bus rated at 533 MHz and 667 MHz.  It is possible to use faster memory as you have discovered, but the maximum memory clock is determined by the data bus of the computer.  You can install memory rated for a lower speed than the speed defined by the data bus and the memory clock will slow to a lower speed that is compatible with the installed memory, but using memory rated for a higher speed will not result in a clock speed higher than the max for the data bus.

Why does Dell even sell the 800mghz if it knows that the data bus only goes to 667mghz...rhetorical.  

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