Virtualization represents any type of process obfuscation where a process is removed from its physical operating environment. Because of this broad definition, virtualization can almost be applied to any and all parts of IT assets. For example, mobile device emulators are a form of virtualization because the hardware platform normally required to run the mobile operating system has been emulated, removing the OS binding from the hardware it was written for.
But for the real life perspective virtualization can be classified as:
Operating System VirtualizationThis is the most prevalent form of virtualization because of the need of running multiple operating systems on a single hardware.
In this form of virtualization, Virtual Machine Managers (VMMs) manage each virtual machine individually on a host operating system (some time directly on hardware). In turn each Virtual Machine hosts a separate instance of operating system. Each of these separate operating systems instances is unaware of the other.
Application Server VirtualizationApplication Server Virtualization is just glamorous name of advance load balancing specifically of reverse proxy.
This is an example of one-to-many virtualization: one server is presented to the world, hiding the availability of multiple servers behind a reverse proxy.
Application VirtualizationApplication virtualization can be of three types. One way is using Thin Client – browser based access to application. The second one is Zero Client – remote access of machine which hosts application via remote access mechanism. The third approach involves mechanism where application is hosted at remote machine but is executed locally.
Hardware VirtualizationHardware virtualization has roots in parallel processing. With advent of multi processing hardware and multi core processor it has become omni present in business.
Hardware virtualization breaks up pieces and locations of physical hardware into independent segments and manages those segments as separate, individual components.
Storage VirtualizationStorage virtualization can be broken up into two general types: block virtualization and file virtualization.
Block virtualization is best summed up by Storage Area Network (SAN) and Network Attached Storage (NAS) technologies: distributed storage networks that appear to be single physical devices.
File virtualization moves the virtual layer up into the more human-consumable file and directory structure level. Most file virtualization technologies sit in front of storage networks and keep track of which files and directories reside on which storage devices, maintaining global mappings of file locations.
Service VirtualizationService virtualization is like catch all case for all of the above definitions. Service virtualization connects all of the components utilized in delivering a service over the network.
In SOA service virtualization is confined to software aspect only is primarily achieved using ESB.
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