Consider the following scenario:
You have a system with 1GB or greater of Video memory, and 4GB or greater of system memory (RAM).
You run the Direct-X Diagnostics tool, and it reports that you have an unexpectedly low amount of Approximate Total Memory on the display tab.
You may also see issues with some games or applications not allowing you to select the highest detail settings.
On a system with 1GB of video memory, the following values are returned with the associated system memory:
System Memory Reported Approximate Total Memory