Windows 7 – Is it possible to dual boot two OS’s at the same time?

Is it possible to dual boot two OS’s at the same time?

For example: I’m currently dual booting Ubuntu 11.04 and Windows 7. Ubuntu is running on a single 500gb HDD, Windows 7 is running on 1TB RAID 1 mirror. To switch between the two OS’s, a reboot is required. Is it possible to switch between the two OS’s without a reboot?

NOTE: I’m fully aware of the capabilities of VirtualBox and VMWare Player – I use both. Please don’t answer “Use Virtualization!”

EDIT: If this is not possible can you share why it’s not possible? To me, it doesn’t seem like it would be that difficult. Keep in mind that my vision is unencumbered by knowledge!

Solution:

Most, if not all, mainstream operating systems expect to have exclusive acccess to the host computer’s low-level functionality (eg: hardware, ports etc.) and do not have any concept of sharing with anything else – it just won’t work – so to try and run two OSs simultaneously on the same system requires some form of transparent arbitrator to shield the operating systems from each other – in other words, a virtualization application.