Microsoft Corp. (MSFT) and Zend, a key supplier of tools used to design open-source software that competes with Microsoft Windows programs, said on Tuesday the two companies have struck a long-term partnership.

Bill Hilf, a Microsoft technical strategist, said the Zend deal, a multiyear, multiphase partnership, will ensure PHP programs run on past and future versions of Microsoft Web server software. The pact covers both the established Windows Server 2003 and the upcoming version, code-named Longhorn.

Zend Technologies is an Israeli-American company formed to commercialize PHP, the most popular scripting language used by software programmers to build open source Web applications that pose a growing challenge to Microsoft's Windows franchise. PHP runs some of the world's most popular blogs and the Wikipedia.

"PHP has always worked on Windows. The problem is that it never performed very well," Andi Gutmans, Zend's co-founder and chief technology officer, said in an interview.

Twelve-year-old PHP runs on more than 22 million Web sites and is used inside 15,000 companies.

Technical improvements by Zend and Microsoft to make it easier to run PHP on Windows computers will be available to PHP's active base of contributors for further enhancement, starting in the first quarter of 2007.

Rather than marking a sudden change of course, Microsoft is openly engaging in a dialogue with Zend, a key open source promoter, and millions of PHP developers, analysts said.

"It is mostly about Microsoft being competitive," said Stephen O'Grady, an analyst with software analyst firm Redmonk in Denver.

PHP is one popular constituent of the so-called LAMP stack, a collection of independently developed open-source software programs that when packaged together represent an alternative to Microsoft Windows for building complex business applications.

LAMP is an acronym for the Linux operating system, Apache Web server software, the MySQL database and PHP. PHP is the most popular way of programming open-source Web-based software.

"Microsoft is giving corporate software developers one more reason not to choose Linux," said Gartner Inc. analyst Mark Driver, who is based in Minneapolis, Minnesota.

For the 4.5 million software developers using PHP, the partnership represents a victory for pragmatism, industry analysts said.

However, while corporate programmers aspire to embrace the trend toward open-source software design, the mass of developers operate in hybrid settings where software, even open-source programs, often run on Windows server machines.

Three-quarters of Zend PHP customers run applications on Windows, according to Gutmans. The deal with Microsoft "drops the wall for a lot of people to bring PHP applications they are building today over to Windows," he said.

This marks a break from the aloofness that has characterized Microsoft's relations with open source projects. That cool stance forced developers wanting to use PHP software to automatically choose open-source software over Microsoft.

By making PHP applications like SugarCRM, a fast-growing open-source sales and marketing software tool, run as efficiently on Windows-based computers as it does on rival Linux computers, Microsoft can stanch such defections.

It's also a rearguard action to protect Microsoft's server business. Its Server & Tools division is the third-largest of six business segments, contributing 23 percent of Microsoft's revenue of $10.8 billion during the latest quarter.