Usually, system virtualization refers to one of two things; computer system virtualization or operating system virtualization. Computer virtualization centers on using software to create a virtual computer system. Operating system virtualization is creating virtual instances of an operating environment. These instances often run on top of other systems or export to a virtual computer system. In either case, the technology centers on creating software that emulates a hardware computer system.
Virtualization technology has been around since the 60s. In the early days, computers used software to emulate machine operations and create low-level resources, such as memory. These early virtual programs were hampered by the relatively low power of that era's computers. It wasn’t until the late 90s that virtual systems began to really take off. The increase in computing power, access to high-speed data transfer and widespread use of multi-cored processors allowed complete system virtualization to become a reality.
A virtual computer system can be anything from a server to a desktop workstation. In whatever form, the computer system works in a similar manner—a single hardware computer runs a program that effectively splits the system into multiple parts. Each part has a fully functioning operating system installed or virtually connected to it. The overall program oversees each of the individual parts, but outside of that, each section operates as an independent machine.
What happens then depends on the purpose of the virtualized machine. A virtual server acts just like a normal server. Other computers and systems connect to it, often without even knowing that the system isn’t ‘real.’ A virtual desktop system will typically connect to a remote workstation that is specially equipped to handle a virtual workspace. The desktop will be accessible from any pre-designated location, allowing a worker to access her individual computer from multiple places.
Operating system virtualization involves virtual servers or desktops connecting to a single version of an operating system and creating a virtual copy on top of their virtual program. In this case, a user would sit down at his station and connect to a virtual server that would in turn connect to a virtual version of the operating system and send it to the user. The other common reason for operating system virtualization is in hosting environments. When a computer acts as an Internet host, it contains the accounts of many users on one system. Each of these users requires full access to the systems provided by the operating system, but not the resources of the other accounts—by creating a virtual operating system for the system as a whole, the accounts can access what they need without impairing the security of the other accounts.