Microsoft on Wednesday will announce that a long-awaited high-end version of its Windows XP operating system, intended to compete with Unix, is entering customer testing. The 64-bit operating system will be made available on a limited basis bundled with servers using Intel's Itanium processor, said sources familiar with the announcement. Itanium, Intel's long-anticipated and much-delayed successor to the Pentium processor, moves computers to a 64-bit architecture from 32-bit. New 64-bit systems can accomplish roughly double the amount of work 32-bit systems in a given amount of time. Major computer manufacturers including Compaq Computer, Dell Computer, Hewlett-Packard and IBM have shown off early versions of Itanium systems over the last couple of months. For Microsoft, the early test version of 64-bit Windows is a milestone, as the company also prepares for the launch of 32-bit Windows XP on 25 October. More importantly, it clears the way for the company to cue up its 64-bit applications, such as its SQL Server database, for testing. The chip, and computers containing it, will compete against more expensive Reduced Instruction Set Computing (RISC) servers and workstations running Unix. Those systems are sold by Sun Microsystems, IBM, and other makers. While Itanium has long been anticipated, its arrival may be muted, despite the availability of 64-bit Windows XP. Intel on Wednesday acknowledged the chip, which initially will be used in PC workstations and servers, and telecommunications servers, is merely a way station to its successor, McKinley, due out next year. With the delivery of 64-bit Windows XP, computer makers can finally start selling Itanium-based systems, which initially are expected to be used for more demanding applications. While Linux and other operating systems will also be available for Itanium, sources close to Intel say the company is banking on Windows and its huge market share to drive sales. Beyond testing, real-world use may have to wait until 64-bit applications reach the market. While Itanium will run 32-bit applications in emulation mode -- a way of simulating older processors -- testers report unsatisfactory performance. Dell on Tuesday launched its first Itanium server, the PowerEdge 7150, which will be available by August. See Chips Central for the latest on processors and the semiconductor industry. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the Chips Central forum Let the editors know what you think in the Mailroom. And read other letters.