Can I take a Hard Drive out of a Desktop/ Laptop computer and use it as a Virtual Machine without converting it?

Question

Without converting the Hard drive to an ISO or P2V format, is it possible to use a physical hard drive plugged in via USB as a Virtual Machine?

(Virtual Box is ideal, but not essential)

Answer 1

For VirtualBox, please refer to http://www.virtualbox.org/manual/ch09.html#rawdisk:

Starting with version 1.4, as an alternative to using virtual disk images (as described in detail in Chapter 5, Virtual storage), VirtualBox can also present either entire physical hard disks or selected partitions thereof as virtual disks to virtual machines.

Note that this process involves creating a VMDK image file, but the file doesn't actually contain any data, but just the metadata referring to the disk or partition that you're pointing to.

Please also note that when you attempt to boot this, it will not be much different than moving the hard drive from one physical computer to another - one with different hardware (chipset / CPU / etc.). This will require your OS (you didn't mention what you're using) to be able to properly detect and install any appropriate drivers for the new virtual hardware that will be presented by VirtualBox. This may also cause similar difficulties if you attempt to use the drive natively again. Finally, be sure to heed the warning shown on this page:

Raw hard disk access is for expert users only. Incorrect use or use of an outdated configuration can lead to total loss of data on the physical disk. Most importantly, do not attempt to boot the partition with the currently running host operating system in a guest. This will lead to severe data corruption.