The forthcoming autobiography from Linus Torvalds, creator of the Linux operating system and figurehead of the open source movement, Just For Fun, promises to cast a shadow over Apple's newly released OS X, which Torvalds describes in less than flattering terms. "Frankly, I think it's a piece of crap," Torvalds says of Mach, the microkernel on which Apple's new operating system is based. "It contains all the design mistakes you can make, and manages to even make up a few of its own." Torvald's comments promise to upset not just Apple fanatics, but also some quarters of the free software movement. The Mach microkernel is also being used as the core of Hurd, a kernel project from the Free Software Foundation that will be an alternative to Linux as the heart of the GNU (Gnu's Not Unix) operating system, originally devised by free software advocate Richard Stallman. The criticism comes in a chapter where Torvalds tells that, on arrival in Silicon Valley in early 1997, Apple's charismatic chief executive Steve Jobs invited him to join Apple and help develop OS X. He says that Jobs was also keen for him to help attract open source developers to the project. The remarks will particularly sting Apple, because the company has made great play of the fact that the core of its new operating system is, like Linux, based on the Unix operating system and was developed on open source software. The Mach microkernel was created at Carnegie Mellon University in 1985 and has been incorporated into a number of commercial operating systems including IBM's OS/2 on certain platforms and Apple's OS X. Torvalds says that as developers have tried to improve the Mach microkernel it has become hugely complicated and convoluted. OS X has not been unanimously applauded since its launch. Shortly after it was released to the public two weeks ago, users questioned the lack of support for certain peripherals, particularly CD-rewritable and DVD-recording drvies, suggesting that the operating system might be under-ripe. Torvalds says that, even back in 1997, he foresaw compatibility problems between the new operating system and legacy applications, due to a lack of memory protection -- a safeguard that stops applications influencing each other and the operating system -- in old Mac applications. According to Torvalds, Jobs assumed that he would be interested in joining Apple's mission to capture more of the personal computer market from Microsoft, rather than continue concentrating on Linux. "I don't think Jobs realised that Linux would potentially have more users than Apple, although it's a very different user base." Apple was not available for comment at time of posting. Take me to the Linux Lounge Have your say instantly, and see what others have said. Click on the TalkBack button and go to the ZDNet news forum. Let the editors know what you think in the Mailroom. And read other letters.