Thats because Vista is supposed to be an OS, i.e. it's not supposed to consume the resources, but rather only provide services for the apps that *are* supposed to be using the majority of the system resources. A game being 2-5Gb is understandable, as it contains a lot of graphics and textures, and games are supposed to have those. An OS is not a game... it doesn't require any fancy graphics and textures.A video is already compressed with lossy compression, a sacrifice of quality vs size. The same with MP3s. But those are simply data and not programs.