Bill Gates has embarked on his latest anti-Linux campaign, stressing in an e-mail ostensibly to customers, that open source and interoperability are not necessarily one and the same.

The industry has attempted many efforts at heterogeneity, Gates said, citing "a strong commitment to interoperability" as the solution. "That means letting different kinds of applications and systems do what they do best, while agreeing on a common 'contract' for how disparate systems can communicate to exchange data with one another."

But, he said, interoperability is sometimes confused with open-source software. By whom, we don't know, but if Bill says so... "Open source is a methodology for licensing and/or developing software - that may or may not be interoperable. Additionally, the open source development approach encourages the creation of many permutations of the same type of software application, which could add implementation and testing overhead to interoperability efforts," he continued.

The careful inclusion of "may" or "could" will almost certainly leave Gates open to attacks of spreading FUD - fear, uncertaintly and doubt - about his open-source rivals. Many of them will also be able to point that when it comes to interoperability, Microsoft has traditionally done everything in its power to keep it a family affair.

Microsoft continues to maintain its code in a proprietary, commercial format and despite court judgements ordering to open parts of its code up, keeps tight control of it.

But Gates also wanted to outline Microsoft's latest strategy. "Today I want to focus on two major thrusts of Microsoft's product interoperability strategy: First, we continue to support customers' needs for software that works well with what they have today. Second, we are working with the industry to define a new generation of software and Web services based on eXtensible Markup Language (XML), which enables software to efficiently share information and opens the door to a greater degree of 'interoperability by design' across many different kinds of software."

Continuing on his interoperability soapbox, Gates stressed that Microsoft "offers a comprehensive portfolio of interoperability software capabilities, from the operating system to individual applications." He cited a list of systems that Microsoft software will communicate with, including mainframes, minicomputers, and "various Unixes, including Linux".

Previous Gates e-mails have covered topics such as security, anti-spam, and manageability. All have raised eyebrows.