Sun Microsystems VIRTUALBOX 3.0.0 - Manual (Page 42)

3 Starting out with VirtualBox
The difference between these three options is crucial. They mean:
• Save the machine state: With this option, VirtualBox “freezes” the virtual ma-
chine by completely saving its state to your local disk. When you later resume the
VM (by again clicking the “Start” button in the VirtualBox main window), you
will find that the VM continues exactly where it was left off. All your programs
will still be open, and your computer resumes operation.
Saving the state of a virtual machine is thus in some ways similar to suspending
a laptop computer (e.g. by closing its lid).
• Send the shutdown signal. This will send an ACPI shutdown signal to the vir-
tual machine, which has the same effect as if you had pressed the power button
on a real computer. So long as a fairly modern operating system is installed and
running in the VM, this should trigger a proper shutdown mechanism in the VM.
• Power off the machine: With this option, VirtualBox also stops running the
virtual machine, but without saving its state.
This is equivalent to pulling the power plug on a real computer without shutting
it down properly. If you start the machine again after powering it off, your
operating system will have to reboot completely and may begin a lengthy check
of its (virtual) system disks.
As a result, this should not normally be done, since it can potentially cause data
loss or an inconsistent state of the guest system on disk.
The “Discard” button in the main VirtualBox window discards a virtual machine’s
saved state. This has the same effect as powering it off, and the same warnings apply.
3.4.4 Snapshots
With VirtualBox’s snapshots, you can save a particular state of a virtual machine for
later use. At any later time, you can revert to that state, even though you may have
changed the VM considerably since then.
This is particularly useful for making sure that a guest installation is not damaged
by accidental changes, misbehaving software, or viruses.
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