It is sometimes convenient to be able to run Tails without having to restart your computer every time. This is possible using [[!wikipedia Virtual_machine desc="virtual machines"]].
With virtual machines, it is possible to run Tails inside a *host* operating system (Linux, Windows, or macOS). A virtual machine emulates a real computer and its operating system, called a *guest*, which appears in a window on the *host* operating system.
When running Tails in a virtual machine, you can use most features of Tails from your usual operating system, and you can use both Tails and your usual operating system in parallel, without the need to restart the computer.
Traces of your Tails session are likely to be left on the local hard disk. For example, host operating systems usually use swapping (or *paging*) which copies part of the RAM to the hard disk.