Microsoft has released its Virtual PC 2004 software as a free download. 

The PC emulation package allows users to run multiple operating systems on a host PC, making it suitable for software developers and testers. The software previously cost around £90.

Explaining the rationale behind the decision on the MSDN Virtual PC blog, Ben Armstrong, a programme manager on the Virtual Machine team at Microsoft, wrote: "Microsoft views virtualization as a tool. Virtual PC is used for a number of reasons, but primarily for development and test scenarios and application compatibility. 

"We already provide Virtual PC as part of MSDN for development and test users and, given that all our other application compatibility tools are free, charging for Virtual PC did not make much sense."  

Virtual PC 2004 supports Microsoft operating systems from MS-DOS up to Windows XP. Vista is not officially supported, but can be made to run providing that a few steps are followed. 

Virtual PC 2004 is built on virtualisation technology that Microsoft acquired in February 2003 from Connectix.