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among the many virtual machines through the guest operating systems. This is a
level of complexity an OS does not have. The operating system only deals with the
applications running on top of it. It does not have to deal with the complex needs
of another operating system.
Definition
Guest operating system
—The operating system that runs on a virtual machine.
Figure 3.2
illustrates the same environment when it is virtualized. Sitting on the physical
host is the hypervisor. The hypervisor's job is to provide physical resources such as
CPU, memory, and disk to its customers. Its customers are the many guest OSs running
on the virtual machines.
Figure 3.2
Three physical hosts after virtualization.
A virtualized infrastructure uses a many-to-one relationship: There are many
applications running on a server or physical host. A natural byproduct of working this
way is the use of resources such as CPU, memory, and disk much more efficiently. No
longer will you live in a world of 8%-12% average utilization that is caused by having
every system sit on a different physical server.
What Is a Virtual Machine?
Think of a virtual machine (VM) as a software-based partition of a computer. It is not
emulation at all because it passes through the CPU instructions directly to the
