1GB RAM only 512MB being used

[theHerbs]

hey,
i have a ECS K7VTA3 v6 motherboard. the manual says it can accommodate 2 DDR SDRAM modules up to 1GB each; total memory capacity 2GB.

i have one 1GB module installed, but its only posting 512MB.

Its doing this on Windows98 SE and Winows Xp Pro

can anyone help me?