Datasheet

Chapter 1: Overview of Virtualization

these software packages, see the section “ Other Popular Virtualization Software ” in the next

chapter.

Guest OS: Virtual machines run within an application that is running as a standard application

under the operating system that executes on the physical host system. This application manages

the virtual machines, mediates access to the hardware resources on the physical host system,

and intercepts and handles any privileged or protected instructions issued by the virtual

machines. Figure 1 - 2 illustrates this approach to virtualization. This type of virtualization

typically runs virtual machines whose operating system, libraries, and utilities have been

compiled for the same type of processor and instruction set as the physical machine on which

the virtual systems are running. However, it can also run virtual machines, libraries, and utilities

that have been compiled for other processors if the virtualization application can perform

instruction-set translation or emulation, as is the case with products such as Microsoft ’ s Virtual

PC product. For more information about this approach to virtualization and some examples of

virtualization software that uses this approach, see the section “ Server or Machine

Virtualization ” earlier in this chapter. For details on any of these software packages, see the

section “ Other Popular Virtualization Software ” in the next chapter.

❑

Host Operating System

Virtualization Application

Hardware

Guest OS/Virtual Machine

Figure 1-2

Hypervisor: A hypervisor is a low - level virtual machine monitor that loads during the boot

process, before the virtual machines, and runs directly on the physical hardware, as shown in

Figure 1 - 3 . The hypervisor handles requests for access to hardware resources on the physical

host system, traps and handles protected or privileged instructions, and so on. Hypervisor -

based virtualization runs virtual machines whose operating system, libraries, and utilities have

been compiled for the same hardware and instruction set as the physical machine on which the

virtual systems are running.

❑

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