Shared memory

Can some one please explain to me in small easy to understand words [smiley=laugh.gif] what the following is and what it does please. The reason is, I have a GeForce 7300 SE 512mb. Can I disable the shared RAM with this setting so I do not loose 256mb of my "normal" RAM
VGA share memory size. (BIOS setting)
Thanks
Matt
VGA share memory size. (BIOS setting)
Thanks
Matt