Windows XP won't make its formal bow until October 25, but its 64-bit big brother is quietly launching on a small group of high-end computers. Windows for Itanium (Intel Corp's first 64-bit CPU) is Microsoft's first venture into 64-bit computing, a market long dominated by companies like Sun and SGI. Itanium and 64-bit Windows represent the next generation of Wintel computing – but it's a future that most people won't see for a while. The new OS won't be sold in stores. Instead, both server and workstation versions will come preinstalled on high-end Itanium-based computers. And since both versions will only be finalized alongside their respective 32-bit Windows XP counterparts, early Itanium adopters will basically get interim versions with support from Microsoft and free upgrades to final code. That code is due on October 25 for the workstation (called Windows XP 64-Bit Edition) and three to six months later for servers (dubbed Windows Advanced Server Limited Edition; the final names aren't set). The reason for the early release is most likely to stop other OSs that can already run on 64-bit systems, such as Linux, eating into Microsoft’s hoped-for market share on Itanium. Microsoft has been engaged in a long running war again vendors selling ‘naked’ Intel-based computers – and there has been much argument over whether its definition of a ‘naked’ machine is one without any OS, or just one without Windows. The 64-bit Windows servers are intended for ecommerce, huge databases, or other applications that need more data-crunching muscle than they can get from Xeon or Pentium systems running Microsoft's existing 32-bit servers or its upcoming XP lines. Windows XP 64-bit workstations are expected to cost £4,000 and up; they're geared toward such computation-intensive tasks as high-end engineering design and modeling, and professional video editing. Since commercial 64-bit applications won't be available at launch, the first systems – from HP, Dell, Compaq, and IBM – will go to customers who want to create custom or commercial 64-bit apps. One major selling point, at least from Microsoft's perspective: 64-bit Windows will run most existing 32-bit Windows apps, so engineers and developers who previously used a Sun UltraSparc or HP-UX box for their core tasks and a Windows PC for Microsoft Office could do everything on one machine from now on. But because 64-bit Windows has to emulate the 32-bit version to run 32-bit apps, the apps' performance will be slower on a 64-bit machine than on a Pentium III PC of comparable clock speed (Itanium launched at 733 and 800 MHz). And according to analyst Chris LeTocq of Guernsey Research, most engineers will not want to slow down their workstations with 32-bit apps. Windows for Itanium won't support DOS or Windows 3.x applications either, and it is not expected to include such Windows XP features as Netmeeting and power management sleep states. Some of these elements may resurface as 64-bit computing trickles to consumers, but LeTocq says he doesn't expect that to happen for another three to five years.