Gartner singled out virtualization is the top strategic technology for 2009 at its Symposium/ITxpo this week, restating what it said six months ago when it identified virtualization as the highest-impact trend changing infrastructure and operations through 2012.

Cloud computing is second on Gartner’s list.

Cloud computing has never been on the annual list before. Now it’s a platform for SaaS, infrastructure, content and business processes, reduces the barrier to entry, scales and lets business grow faster.

Gartner thinks 80% of the Fortune 1000 will be using clouds in one way or another in the next three or four years.

Virtualization was Gartner’s number five pick last year. It was moved to the top because it seems to be touching everything and, like clouds, is a recourse in times of economic downturn.

It will transform how IT is managed, what is bought, how it is deployed, how companies plan and how they are charged.

It’s also supposed to create a new wave of competition among infrastructure vendors that disrupts and consolidates the market over the next few years.

There’s a strategic advantage in early adoption. Server virtualization is in progress; the opportunity is in storage and PCs.

Gartner figures that virtualization reduced the x86 server market by 4% in 2006 and has predicted that more than four million virtual machines will be installed on x86 servers by 2009.

It expects the number of virtualized PCs to grow from less than five million in 2007 to 660 million by 2011.

Virtualizing PCs means breaking the dependencies between the hardware and the operating system (machine virtualization) and between the operating system and applications (application virtualization).

Gartner thinks machine virtualization will have the bigger impact, making personal computing more manageable, flexible and secure by allowing multiple individual footprints to be defined on the same device.

Gartner distinguished analyst Thomas Bittman has said, “Essentially, virtualization creates a fork in the road for operating systems. Traditionally the operating system has been the center of gravity for client and server computing, but new technologies, new modes of computing, and infrastructure virtualization and automation are changing the architecture and role of the operating system. The days of the monolithic, general-purpose operating system will soon be over.”

Heady stuff.