The newest and next versions of Windows – XP Professional x64 Edition and Longhorn – will share centre stage this week at WinHEC, Microsoft's annual Windows Hardware Engineering Conference.

Both versions are expected to figure prominently in Microsoft chairman and chief software architect Bill Gates' keynote address previewing the third decade of Windows, the operating system that was launched in late 1985.

WinHEC, a conference where Microsoft previews its software for PC makers and other hardware designers, this year doubles as the launch event for XP Pro x64, Microsoft's first operating system for desktop computers powered by 64-bit CPUs. (To read our review of this final version of the OS, click here.)

Microsoft is also launching three 64bit server OSs: Microsoft Windows Server 2003 Standard x64 Edition, Microsoft Windows Server 2003 Enterprise x64 Edition, and Microsoft Windows Server 2003 Datacenter x64 Edition.

Conference attendees will also receive preview code of Longhorn, the next version of Windows. The beta program is scheduled to appear this summer with the full version to follow in the second half of 2006.

Microsoft says a number of vendors will be announcing systems with x64 (either the desktop or one of the server editions) pre-installed, including Acer, AlienWare, Dell, FSC, Fujitsu, HP, Hitachi, IBM, NEC, and Unisys.

Individuals who already own 64bit PCs running the 32bit version of Windows XP Professional have until July 30 to replace it with a licensed version of x64 at no charge through Microsoft's Technology Advancement Program. Details will be made available through Microsoft's x64 Web site.

Anyone contemplating an upgrade to x64 will want to make sure their hardware has 64bit support. A number of component vendors were planning on announcing such support at WinHEC.

Microsoft officials previewing Gates' keynote for reporters say that in addition to launching x64, Gates is expected to focus on the increased importance of products enabling mobility, such as tablet PCs powered by Windows XP Professional Tablet PC Edition.

Gates is slated to show several new tablets, including some that cost only £60 more than identical non-tablet products. Additionally, he's expected to show off a reference design for a post-Longhorn ultraportable that has a 9in screen, is no thicker than 10 sheets of paper, and will be operated by pen or voice commands.

Another concept design that Longhorn will support will be a notebook with an auxiliary display on the lid, so that, for example, you could check your calendar without having to boot up the system.

Longhorn will be the first mainstream 64bit OS (a 32bit version will also be available for legacy machines), Microsoft officials say. WinHEC sessions will showcase the OS's new Avalon user interface (which offloads much of the display work to today's increasingly powerful graphics subsystems), data management tools, security, and other features.

People looking ahead to Longhorn's arrival may soon get some guidance on choosing a PC that they'll be able to upgrade. Microsoft plans to announce a program to designate systems as Longhorn-ready. Officials say the requirements will include a current mainstream (or better) CPU, 512MB of RAM, and a graphics subsystem that supports the Longhorn Display Driver Model (LDDM). A Microsoft spokesperson says most graphics board will likely qualify, while some integrated graphics systems that use shared system memory might not.

Additionally, Microsoft plans to announce a two-tiered logo program for peripherals and devices. In addition to the general program that will designate hardware as being Longhorn ready, there will be a "Plus" logo for products that will take full advantage of Longhorn's capability.

Finally, because Longhorn will bring a dramatic new look to Windows, Microsoft is sponsoring a contest for corresponding innovation in PC design. Details are not available, but Microsoft expects that finalists will be announced by the end of this year.