Microsoft has made available the Release Candidate (RC) of Windows 7, marking another milestone on the way to the final availability of its latest operating system. Also available is a beta of Windows XP Mode, a compatibility tool to help users migrating from XP to Windows 7.

Windows 7 RC was made available to download at 2pm UK time on 30 April for IT professionals with a subscription to Microsoft's MSDN or Technet sites. The code will be generally available on 5 May from Microsoft's Windows site.

While the RC code introduces a number of changes from the earlier beta release, many of these are under the hood and will not be noticeable to users.

"We've changed everything from major through to minor, but it won't look a lot different," said John Curran, Windows Business Group lead at Microsoft UK.

Many of the changes are based on customer feedback to the beta release, improving features such as Jump Lists and the multi-touch user interface.

Nevertheless, Microsoft "strongly advises" those running Windows 7 to upgrade, as the RC code is the most polished and is unlikely to change much between now and the release to manufacture (RTM) of the final code.

According to Curran, the two most significant additions with the RC release are the inclusion of the finished build of Internet Explorer 8 (IE8) and the beta of Windows XP Mode. IE8 in earlier Windows 7 releases was beta code that users were unable to upgrade until now.

Windows XP Mode, disclosed earlier this week, will enable consumers and small business customers to run any software not compatible with Windows 7. It is available only for the Professional and Ultimate editions of Windows 7.

XP Mode is based on a forthcoming version of Virtual PC for Windows 7, but has been customised to hide the fact that applications are running in a virtual machine.

"From the start menu [in Windows 7] users will see an XP Mode program group, and will be able to click application icons to launch them just like any other program," said Curran.

Windows XP Mode ships with a pre-packaged Windows XP Professional environment, so that users do not have to install XP or acquire an extra licence.

However, users will have to dive into the XP environment to install applications they wish to run there, unless their PC vendor supplies the machine ready configured.

"The easiest way for a small business to get it is to have the original equipment manufacturer set it up for them," said Curran.

For larger businesses, an updated version of Microsoft Enterprise Desktop Virtualisation will provide the same capabilities, but under administrator control.

Curran said that the finished code of Windows XP Mode will be available at the same time that Windows 7 ships, but he would not be drawn on a specific date, although the RTM is widely expected before the end of 2009.

"As we've said in the past, Windows 7 is on track for delivery within three years of the launch date of Windows Vista. The date will come down to when the code meets our quality bars," he said.