Many people use both Linux and MS-Windows. The ability to do so is an important part of "the Linux revolution"; i.e. letting people experiment with (and get hooked on) Linux while still being able to run their off-the-shelf software. Since both Linux and MS-Windows use virtual memory with swap to disk, a frequently occurring question in comp.os.linux.setup is how to share swap spaces, in order to reduce the amount of disk space needed.
There are several methods for sharing swap spaces, the one described in this document is probably the most complicated one but is the only one I have encountered that allows maximum performance for both environments without the risk of trashing a disk partition. If you are using DOS, then many DOS applications manage their own swap files. You can also share the Linux swap partition with these applications.