coLinux: Linux for Windows Without Rebooting
Operating system virtualization is popular technology these days. People run different operating systems on top of their existing ones not only for experimental purposes but also for production use. Many different virtualization systems exist. VMware, which runs on both Windows and Linux, may be the best-known proprietary example. It can host many operating systems from Win98 to FreeBSD and different flavors of GNU/Linux.
Of course, the free and open source software communities have their own virtualization software. Bochs follows the example of VMware, while Plex86 also does CPU virtualization.
For cases in which you'd rather run different versions of Linux atop an existing Linux installation, User-mode Linux may be a better answer. It operates at the kernel level and can supply a very stable, try-and-see sandbox for different Linux kernels, with almost no virtualization penalty. Because of this, more and more developers use User-mode Linux to test new kernels, drivers, etc.
What if you want to run GNU/Linux atop a Windows platform or try Linux without installing it on a partition itself, thereby preserving — and not even rebooting — your Windows system? Don't worry; VMware and Virtual PC are not your only choices. A new free software project called coLinux, or Cooperative Linux, lets you do nearly everything User-mode Linux does on Windows 2000 or XP.
