Where the OS is stored.

[FanceGeek]

Question. If you don't have enough space on your pc or desktop. Though you want another OS perhaps on virtualbox. Can I buy a seperate hard drive, such as a flashdrive or something and when adding a new OS to the virtualbox application, install it on that hard drive, then be able to remove and attach that hard drive to the computer? Like for example when I remove the hard drive, the OS won't load or show up. When I put it back in, it will load and show up?

[mpack]

VM are just files on the host. They can be put anywhere you can put a file.

[FanceGeek]

So for example if I installed virtualbox and added ubuntu, then stored the "Virtualbox VM" folder inside a removable hard drive the OS will show up when I connect the hard drive and won't show up when I disconnect it.

[FanceGeek]

Also will you able to use that removable hard drive as the space.

[mpack]

Are you using "the OS" as a synonym for "the VM"? That makes it a completely different question. VirtualBox will not hide broken VM links - it will show the VM as inaccessible until you plug the removable drive back in and restart VirtualBox.

Incidentally, keeping VMs on a removeable drive is usually not a good idea, if you want reliability.

[BobBib]

You can select the desired folder to store the VMs in the preferences (File -> Preferences... -> General -> Default machine folder:), and it can be located on a secondary or removable drive.
But don't start VirtualBox when that drive is not mounted, or you'll get an error (as mpack has already said).