The first beta version of the next Windows version, codenamed Longhorn, will now not be available until the second half of next year - yet another delay.

Microsoft had originally planned the beta for 2004, but earlier this year said its release would slip into early 2005. Now, it is moving it back again because the much-lauded security update to Windows XP, Service Pack 2 (SP2), is taking so long to piece together.

The first delay of the Longhorn beta was also attributed to work on SP2. A large number of developers working on Longhorn were reassigned to work on SP2, which is due out next month. The work on SP2 and the focus on security essentially set a higher quality bar at Microsoft, sources said.

The beta will be released ahead of a second Longhorn-focused Microsoft Professional Developers Conference (PDC), which the company is planning for the third or fourth quarter of 2005. Microsoft does plan to continue distributing technical preview releases of Longhorn ahead of the beta however.

A later beta could certainly mean a delay for the final product, which is currently expected to be released in 2006. A beta period for Microsoft products typically lasts at least 18 months, but for a major release such as Longhorn the testing period may be extended, as it was for Windows Server 2003.

Longhorn is a major Windows release, and a "big bet", according to Bill Gates. He has also described it as a "big breakthrough release" and the most significant release of Windows since Windows 95. The most recent Windows OS was Windows XP, released in late 2001.