Apple Boot CampHow it works exactly, not so sure. I'm not a Mac user. Perhaps the Mac users here could you on that.
As for Parallel OS, better known as Parallels Desktop, it's a type of virtualization, something like VMWare.
Instead of creating many partitions to load an OS, Parallels allow you to run two or more OS together, one of which is the main, the others are on a virtual partition.
Their product is
here, and some usage is written at
ZDNet.