To use virtual machines, we need software called a hypervisor. A hypervisor manages resources between the host machine and the virtual machines, provides access to disks, and has an interface to manage it all. There are two different types of hypervisors: type-1 and type-2. Type-1 hypervisors are the so-called bare-metal hypervisors. These are installed instead of a regular operating system such as Linux, macOS, or Windows, directly on the hardware. These types of hypervisors are used for corporate servers, cloud services, and so on. For this book, we will use a type-2 hypervisor (also called hosted hypervisors): these are installed within another operating system, as a piece of software not much different than, for example, a browser.

There are many type-2 hypervisors. The most popular choices at the time of writing are VirtualBox, VMware workstation player, or OS-specific variants such as QEMU/KVM on Linux, Parallels Desktop on macOS, and Hyper-V on Windows. Because we are going to use a virtual machine throughout this book, we do not assume anything about the host machine: you should work comfortably with whatever operating system you prefer. Because of this, we've chosen to use VirtualBox as our hypervisor, since it runs on Linux, macOS, and Windows (and even others!). Furthermore, VirtualBox is free and open source software, which means you can just download and use it.

Presently, VirtualBox is owned by Oracle. You can download the installer for VirtualBox from https://www.virtualbox.org/. Installation should not be hard; follow the instructions by the installer.