Is Intel GMA 4500 less than 512 MB? Can you explain ?

As said, such "cards" are no longer cards. Gpu's reached a point where they could cram most of the basic 2d low end functions on a chip for super cheap. So low end pc's get them for free on the motherboard, the ram is shared system memory, and thus slow. It doesn't matter because even if it had its own memory or more it wouldn't be able to do anything with it, its just that slow. 512MB or 128MB are meaningless numbers, in windows desktop you don't need anything near that for desktop use. And as said, these things are useless for games, so these are essentially empty marketing specs.