Graphic card gt220 problem?

hello guys.i have a problem with my graphic card gt220. it has total memory 1gb and when i go and check aprx.total memory by typeing dxdiag in "run" it tells me that i have 493mb total aprx memory of graphic card and i suppose to have 1 gb .i don't have anything in my desktop and idont know what the **** is using half of my memory or what is wrong with it.can someone help me?i have asus 5270 desktop computer .please i need your help ...helllppppppppppppp|||your computer is using it most likely