What is Virtualization?

Virtualization and Virtual Machines

Virtualization is the simulation of a computer hardware environment by software. Virtualization software runs "between" the computer hardware and the operating system (Windows, Mac OS, Linux), accepting input from the OS and redirecting it to the appropriate hardware addresses. The virtualization software also does the reverse, catching output from hardware and redirecting it to the appropriate places in the operating system. The beautiful thing is that the operating system doesn't know or care if it's running on physical hardware, or a virtual machine that only exists in the memory space of a computer.

Virtualization enables you to run Windows on a Mac, or Linux or Mac OS on PC. It also enables application software written to run under Windows to be run on a Mac computer. The advantages of virtualization's cross-platform flexibility include the ability to do the following:

• Run older programs under virtualized copies of compatible older operating systems; your Windows 95 game can be played on your Windows 7 computer. Virtualization used this way can save businesses the cost of upgrading applications that work perfectly well to never versions designed for the latest OS.
• Confine applications to a "sealed" virtual machine within a computer's RAM. Confining applications to a secure "sandbox" through virtualization makes it safer to develop and debug applications without corrupting the rest of the system.
• Host multiple Web sites on one physical server under different operating systems. Yes, one machine can have Windows, Linux, and other operating systems running in virtual machines simultaneously, so each Webmaster can have the OS environment of his or her choice. Web hosting firms use virtualization extensively, and so do some large enterprises.

A completely virtualized system of OS and applications can be stored offline in an image file on hard disk or optical media, preserving a snapshot of a "baseline" system. If you want to configure a new computer for a new employee, you just copy the image file onto the new computer and it's up and running in the company-standard configuration.

VMWare is one of the most popular virtualization software environments on the market. While it can be used on a home computer, VMWare is really aimed at enterprise systems. Windows 7 comes with virtualization built in, specifically to let users run Windows XP under Windows 7 so they can keep using applications that require XP. See my related artile on Windows 7 XP Mode for more on that. The open source Xen virtualization standard is the source of virtualization applications for servers, desktop/client machines; and cloud computing environments.

Virtualization is touted as a new innovation, but in fact nearly all applications ran in virtualized compartments on mainframe computers decades ago. When I started my career at IBM in the early 1980's, we used two mainframe operating systems: VM (Virtual Machine) and MVS (Multiple Virtual Storage). So you can see why "old-school" IT pros tend to roll their eyes at all the hubbub about virtualization. To them, it's just been rediscovered, not newly discovered.

Are you using virtualization on your PC, Mac or Linux computer? Post your comment or question below...