Fooling the processor

Many a times when we use linux this can be done more easily in windows and vice-versa. So is it possible to run two operating systems together one at a time? Yes using Emulators it is possible. These emulators fools the processor and runs 2 operating systems.

Once upon a time when pen drive is something every person having computer has. And due to falling prices now a days its not even expensive to use a pendrive. So thought of using Qemu along with accelerator kemu and twiking with autorun.inf file, what i made was just inserting a pendrive and then your ubuntu starts without booting the pc.

I don't know much advantages of it. There are many. But memory becomes half the size is the biggest disadvantage.