Virtualization Basics

This lesson will provide an introduction to virtualization on the desktop or server. Topics such as the purpose of virtualization, what a Hypervisor is and how it is used, software that can allow virtualization, and hardware requirements are outlined.

Purpose of Virtualization

Virtualization is a new topic on the A+ certification. Virtualization is used to create a desktop or server inside of an application that runs on a physical machine. Virtualization occurs when a host machine uses its physical resources to host a virtual machine.

The operating system of a virtual machine is independent of the operating system installed on the host machine. Since one physical machine can host multiple virtual machines, virtualization is considered Green IT.

It may provide critical resources such as applications, file-sharing services, and other productivity tools. It also allows a user to run a program that is not available on the host’s operating system. A virtual machine is often called a guest.


A hypervisor is a software that creates and manages a virtual machine on a physical or host machine. It is sometimes referred to as a virtual machine manager (VMM).

A hypervisor can run several virtual machines on one host machine with each virtual machine running the same or different operating systems. The host machine’s hardware resources determine how many virtual machines can be running at one time.

The hypervisor assigns the physical resources to the virtual machine (e.g., processor, memory, hard drive) as it is needed. There are two types of hypervisors:

  1. A Type 1 or native hypervisor allows a guest OS to use physical resources on the host and to manage how the host’s resources are allocated to guest operating systems. Think of this as a virtualized host operating system.
  2. A Type 2 or hosted hypervisor is hosted inside another operating system. Think of this as one operating system hosting another.

Virtual Software

Virtualization software allows a single host computer to create and run multiple virtual environments. Several companies make virtual software for both desktops and servers. Common server virtualization includes:

  1. Windows Hyper-V
  2. VMware vSphere

Common desktop virtualization includes:

  1. Windows Virtual PC
  2. VMWare Workstation (PC)
  3. Oracle VirtualBox (PC)
  4. VMware Fusion (Mac)
  5. Parallels (Mac)

Virtual PC

Virtual PC has been around for many years for virtualizing Windows desktop environments. It is a type 2 hypervisor because it is run from a host operating system. Virtual PC allows a user to divide system resources from the host Windows operating system among virtual machines running Windows 7, Windows Vista, and/or Windows XP.

XP Mode

Windows XP mode was created so Windows 7 could run Windows XP software. It is available in Windows 7 Professional and higher. It allows a user to run Windows XP programs inside of Windows 7. A fully functional version of Windows XP is opened in a virtual machine on Windows 7 when the XP program starts.

After installation, a program in Windows XP mode can be accessed from the Windows 7 start menu. When a user starts an XP program, XP mode starts up in the background and runs the program. It looks like the program is running natively in Windows 7. It is not built-in to Windows 7 but can be downloaded for free from the Microsoft Windows website.

Host Machine Requirements

The host machine must meet basic system requirements to run virtualization. It must have at least a 1 GHz processor, 15 GB of hard drive space per virtual machine, a virtual network adapter, and support super VGA graphics. The host machine must have a minimum of 2 GB of RAM.

Table 1: Host Machine Requirements

Hardware Requirements
Processor 1 GHz or higher
32-bit or 64-bit OS
Hard Drive Space 15 GB per virtual machine
Memory 2 GB
Networking Virtual network adaptor
Video Super VGA or higher

Virtual Machine Requirements

Virtual machines must meet the basic system requirements of a typical operating system. The more virtualized machines that are run the more RAM that is required. A good rule of thumb is, each virtualized machine needs 1 GB of RAM, plus 1 GB for the host.

Table 2: Virtual Machine Requirements

Virtual OS Minimum Hard Disk Space Minimum Memory
Windows 98 500 MB 64 MB
Windows ME 2 GB 96 MB
Windows 2000 2 GB 96 MB
Windows XP 2 GB 128 MB
Windows Vista 15 GB 512 MB
Windows 7 20 GB 1 GB

Virtual machines are susceptible to malicious attacks just like physical machines. Therefore antivirus and security software is required, Windows updates should be installed, drivers should be updated, firewalls should be used, and programs should be updated on a regular basis.


In this lesson, you learned important concepts about relating to Virtualization. Keep the following in mind:

  • Virtualization allows a user to install more than one operating system on a host machine to be run simultaneously. This process reduces the need for as much hardware, conserves on the size of space needed to house that hardware, and can reduce costs related to running multiple systems, e.g., a power to run and cool the machines.
  • A hypervisor, the software used to create and manage virtual machines, can be installed on top of another operating system such as Windows 7 or Windows Server (Type 2), or it can be installed directly on the hardware as the host operating system (Type 1).
  • Several applications can be used to virtualize servers and/or desktops. The most commonly used applications in a corporate environment are VMware’s vSphere and Microsoft’s Hyper-V. Virtualization software most commonly used on the desktop are Windows Virtual PC, VMware Workstation, and Oracle’s Virtual Box. VMware Fusion and Parallels are used on the Mac.
  • So that backward-compatibility can be maintained, Windows 7 included what is called XP Mode. Applications that were not yet updated to run on Windows 7 can still be used – in XP Mode.
  • Just as before, when installing an operating system on a machine, know the hardware requirements needed for a host that will house virtualized machines. What hardware is needed for a virtual machine’s installation is also required.