[kahrguy]

I have a external hard drive can I boot up two
operating system at a same time and switch back
and forth??
Is there a software for it??

Thanks

[Washington,D.C.]

If they are both Windows of some sort can use Restart

http://majorgeeks.com/Restart_d709.html


If your PC will boot from USB you can set it as first boot(in BIOS),then when external drive is hooked up can boot it,when not present will boot from internal drive((as long as internal hard drive still in boot menu).