Running a virtualised version of Windows XP on a Windows 7 PC can be useful for running legacy software programs. But the most popular way of doing so limits you to 32bit XP, and therefore on 3GB RAM. Here's how to run 64bit Windows XP on a Windows 7 PC or laptop.

QUESTION I'm looking to build a PC for use as a Windows 7 Professional CAD workstation. It will probably have 8- or 16GB of RAM. I have legacy software running on XP. Can you tell me if all the RAM will be available in XP Mode? Anon

HELPROOM ANSWER The Windows XP emulation mode offered with Windows 7 Professional runs a 32bit version of XP. The maximum amount of memory available to the guest operating system is 3,712MB.

If you use another virtualisation program, such as the free VirtualBox from Oracle, you will be able to run 64bit guest operating systems, including Windows XP 64bit. However, you will need to purchase a copy of Windows XP 64bit to do so.

It's important to consider that with both options, your virtual Windows XP PC will use a pre-allocated chunk of system memory from your host PC. You wouldn't want to allocate too much system memory to XP Mode, since it would deplete the resources of your host Windows 7 operating system.

You don't say which legacy applications you need to run under XP. If it's your CAD applications that require XP, we recommend setting up a dual-boot system that allows you to run a native installation of XP at full speed. The graphics capabilities of a virtual Windows XP installation will be considerably slower than a native installation.

Given enough disk space, you could install both a dual-boot system and a virtualised system. This would enable you
to conveniently run your XP applications without rebooting, but with the option of booting into your native XP installation for intensive sessions where performance is key.

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