When dealing with virtualization, and also for understanding the following chapters of this documentation, it helps to acquaint yourself with some important terminology, especially the following terms:

• Host operating system (host OS). This is the OS of the physical computer on which was installed. There are versions of for Windows, macOS, Linux, and Oracle Solaris hosts. See .

  Most of the time, this user guide discusses all versions together. There may be platform-specific differences which we will point out where appropriate.

• Guest operating system (guest OS). This is the OS that is running inside the virtual machine. Theoretically, can run any x86 OS such as DOS, Windows, OS/2, FreeBSD, and OpenBSD on an x86 host. But to achieve near-native performance of the guest code on your machine, we had to go through a lot of optimizations that are specific to certain OSs. So while your favorite OS may run as a guest, we officially support and optimize for a select few, which include the most common OSs.

  See .

• Virtual machine (VM). This is the special environment that creates for your guest OS while it is running. In other words, you run your guest OS in a VM. Normally, a VM is shown as a window on your computer's desktop. Depending on which of the various frontends of you use, the VM might be shown in full screen mode or remotely on another computer.

  Internally, treats a VM as a set of parameters that specify its behavior. Some parameters describe hardware settings, such as the amount of memory and number of CPUs assigned. Other parameters describe the state information, such as whether the VM is running or saved.

  You can view these VM settings in , in the Settings window, and by running the VBoxManage command. See .

• Guest Additions. This refers to special software packages which are shipped with but designed to be installed inside a VM to improve performance of the guest OS and to add extra features. See .