When you click the Close button of your virtual machine window, at the top right of the window, just like you would close any other window on your system, asks you whether you want to save or power off the VM. As a shortcut, you can also press Host key + Q.

The difference between the three options is crucial. They mean the following:

• Save the machine state: With this option, freezes the virtual machine by completely saving its state to your local disk.

  When you start the VM again later, 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 by closing its lid.

• Send the shutdown signal. This will send an ACPI shutdown signal to the virtual machine, which has the same effect as if you had pressed the power button on a real computer. This should trigger a proper shutdown mechanism from within the VM.

• Power off the machine: With this option, 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 OS 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.

  As an exception, if your virtual machine has any snapshots, see , you can use this option to quickly restore the current snapshot of the virtual machine. In that case, powering off the machine will discard the current state and any changes made since the previous snapshot was taken will be lost.

The Discard button in the window discards a virtual machine's saved state. This has the same effect as powering it off, and the same warnings apply.