Think your a bit confused,
The dedicated is the memory on board the graphics card it`s self.
Because you have 8gb of memory and a 64 bit version of windows.
Windows 8 will be using about 4gb of memory when the OS is running.
Don`t forget windows is always resident in memory once it has loaded from the hard drive.
The value left is what is free out of the memory once windows has loaded, to run other programs or games ect.