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For how to install Windows Server 2019 on VirtualBox, see the following link. The operating system you install within VirtualBox (virtual machine) is called the guest.
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VirtualBox terminology, the operating system on which VirtualBox is installed is referred to as the host.
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VirtualBox is a software virtualization package that you can install on your operating system. It installs on your existing Intel or AMD-based computers, whether they are running Windows, Mac, and Linux operating systems. Oracle VirtualBox is a cross-platform virtualization application.
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