A: Swapfile.sys is a system controller file, normally around 256MB. It's used by Metro style applications that don't fit the traditional paging characteristics (such as usage pattern, growth, space reservation) of pagefile.sys. One example of swapfile.sys usage is the suspend/resume of Metro-style applications; however, this is not the only use.

One case where swapfile.sys isn't used is in the fast startup process of Windows 8, which uses the hiberfil.sys for the storage of the kernel session that's maintained between normal reboots (as documented by Microsoft).

Learn more from "Top 10 New Features in Windows 8" and "Q: If I enable Secure Boot on my Windows 8 machine, can I still dual-boot?"