A beta version of Windows XP that runs on desktops or workstations using AMD's Athlon 64 or Opteron processors is now available to the public.

The beta version of XP for AMD's chips was made available to Microsoft's developer network at the launch of the Athlon 64 processor in September. As of Tuesday, any user of a PC or workstation with AMD's new processors can sign up to receive the beta version at Microsoft's website through the customer preview programme.

Potential customers need to pay shipping fees for a CD-ROM version of the beta, but it is available for free if downloaded from Microsoft's site, the company said.

A full version of Windows XP had been expected in the first half of this year when AMD released the Athlon 64. AMD and Microsoft now expect that software to arrive in the second half of the year.

Current Athlon 64 and Opteron users run 32bit versions of Windows on PCs with those chips. But they cannot take advantage of the chip's 64bit capabilities without a 64bit operating system and applications tailored for AMD's 64bit extensions.

A few 64bit versions of Linux are available for desktops, but there are not many 64bit applications available right now. That is expected to change once Microsoft releases the full version of Windows XP.

Sources have said that Intel is preparing a processor that uses 64bit extensions, but the company has not commented on whether that chip will be compatible with AMD's technology.