Database Reference
In-Depth Information
Figure 12-29
The Virtual Machine
Environment
The hypervisor runs
a user application
Virtual
Machine 1
Virtual
Machine 2
User applications
besides the hypervisor
and the virtual
machines it supports
can be run on the
computer
User App 1
User App 2
Hypervisor
Computer Operating System
Computer Hardware
(a) Shared Hardware
The hypervisor runs as
the only application—
there are no other user
applications running on
this hardware
Virtual
Machine 1
Virtual
Machine 2
Virtual
Machine 3
Virtual
Machine 4
Hypervisor
Computer Operating System
Computer Hardware
(b) Dedicated Hardware
virtual machine has been allocated two Gigabytes of main memory for its use, the hypervisor
is responsible for making sure the actual physical memory is allocated and available to the
virtual machine.
Although there are many variants on exactly how virtual machines are implemented, 9
Figure 12-29 illustrates two standard generic physical/virtual machine setups. Figure 12-29(a)
shows the situation where the host machine is not dedicated to hosting virtual machines, but
also runs other user applications. This is typical of a desktop computer where the user wants
to use, for example, a spreadsheet application (such as Microsoft Excel 2013) and a word pro-
cessing application (such as Microsoft Word 2013), while being able to host virtual machines at
the same time. This can be done using a product such as VMware Workstation (see http://www
.vmware.com/products/workstation/overview.html ) from VMware (see http://www.vmware.com ) ,
which is available for the Windows and Linux operating systems.
Figure 12-29(b) shows the situation where the host machine is dedicated to hosting vir-
tual machines, but also runs other user applications. This is typical of network servers where
the goal is to get as much overall utilization of the hardware resources by sharing them among
many servers, but there are no users running applications on the host machine.
One of the advantages of virtual machines is that in many products you can run various
operating systems in different virtual machines, and none of them has to be the same operat-
ing system that is running on the underlying hardware and supporting the hypervisor. Thus,
9 See the Wikipedia article on comparison of platform virtual machines at http://en.wikipedia.org/wiki/
Comparison_of_platform_virtual_machines .
 
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