Novell ZENWORKS APPLICATION VIRTUALIZATION 8.0 - 04-12-2010 User Manual page 8

Novell ZENworks Application Virtualization
2.5 How is application virtualization different from hardware
virtualization?
Unlike hardware virtualization systems such as Microsoft Virtual PC and VMware, the application virtualization
system works at the application level and virtualizes only those operating system features required for application
execution. This allows virtualized applications to operate extremely efficiently, with essentially the same
performance characteristics as native executables.
Advantages of application virtualization over hardware virtualization include:
Extremely high performance: ZENworks virtual applications execute at essentially the same speed as applications
running natively against the host hardware, with only a small additional memory footprint. On the other hand,
applications running within hardware-virtualized environments experience significant slowdowns and impose a
large memory footprint because the virtual machine includes and virtualizes an entire host operating system.
Dramatically reduced application size: ZENworks virtual applications only require a disk footprint
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proportional to the size of the virtualized application, data, and included components. As a result, ZENworks
virtual applications are typically small enough to be conveniently and quickly downloaded by end-
users. Because hardware virtualization requires inclusion of an entire host operating system image, including
many basic subsystems which will already present on the end-user device, hardware virtualization typically
requires gigabytes of storage per virtual machine.
Ability to run dozens of virtualized applications: Because of its low-overhead characteristics, it is easily

possible to run dozens of concurrent ZENworks virtual environments per processor. Conversely, due to the
high overhead of hardware virtualization, it is generally possible only to run a very small number of hardware-
virtualized environments per processor.
Reduced licensing costs: Because ZENworks virtual applications do not contain a host operating system, it is

not necessary to purchase separate operating system licenses to use a ZENworks virtual application. hardware
virtualization systems require a host operating system in order function, possibly imposing additional
licensing costs and restrictions.
However, hardware virtualization is appropriate in certain specialized scenarios:
Non-Windows operating systems: ZENworks virtual applications execute only on the Windows operating
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system. Hardware virtualization can execute any operating system compatible with the underlying virtualized
hardware, such as Linux.
Kernel mode virtualization: The ZENworks application virtualization engine only virtualizes user-mode
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operating system features, whereas hardware virtualization systems emulate the entire OS stack, including
kernel mode components. Applications requiring device drivers or other non-user-mode software may require
a hardware-virtualized environment to function properly.
You should carefully evaluate the advantages and disadvantages of different virtualization approaches before
deciding on a technology to adopt for your deployment scenario.
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