SEATTLE — Although Longhorn isn't slated to be available until "holiday 2006," some PC users are already wondering what kinds of PCs will be able to run the next version of Windows.

Microsoft officials at the Windows Hardware Engineering Conference (WinHEC) here this week in Seattle attempted to provide some answers, vague as though they were.

In the past, Microsoft used WinHEC to deliver a very detailed set of hardware reference specs to the OEMs who attend the event so that they can build new PCs that would be able to run whichever version of Windows was on tap.

At last year's WinHEC, developer sources said that Microsoft was going to recommend the "average" Longhorn PC feature a dual-core CPU running at 4 to 6GHz; a minimum of 2 gigs of RAM; up to a terabyte of storage; a 1 Gbit built-in, Ethernet-wired port and an 802.11g wireless link; and a graphics processor that runs three times faster than those on the market.

Microsoft declined to comment on the rumored specs and never went public with any recommended Longhorn specs at last year's show.

At this year's WinHEC, Microsoft offered up only the most basic of guidelines as to what PC makers should do to make their PCs "Longhorn-ready." During a session at this week's show, Mark Croft, a group product manager in the Windows product management group, told PC makers that most existing mainstream 32- and 64-bit CPUs from mainstream manufacturers should run Longhorn.

While dual-core CPUs will run Longhorn better, "Longhorn does run on mainstream processors," Croft said.

The only other Longhorn PC requirements that are set in stone are 512 MB or better of RAM and, support for the new Longhorn Display Driver Model (LDDM) in order to handle the operating system's new graphical features.

(Comparatively, Microsoft suggests that users have a 300-MHz CPU and 128 MB of RAM to run Windows XP.)

Support for LDDM doesn't insure that PCs will be able to run Aero, Microsoft's next-generation Longhorn user interface, Croft noted. But PCs that can will be able to avail themselves of features such as dot-per-inch scaling; 3D window management; the thumbnail document previews that Microsoft demonstrated as being part of its built-in Longhorn search technology; and the "Glass" theme. Systems that cannot run Aero are expected to run a "Classic" Windows interface.

Croft drew distinctions between PCs that will be "Longhorn-ready" versus "Longhorn-capable." He told attendees of the packed WinHEC session that "older CPUs with 128 or 256 MB of memory and older graphics will still be capable."

Instead of delivering detailed Longhorn reference specs, Microsoft officials offered a number of suggestions to OEMs for what would make a "great Longhorn PC."

Because Longhorn will make its way into so many different kinds of PCs and devices — ranging from home-entertainment consoles, to mobile Tablets — Russell and Croft did not detail any kind comprehensive list of reference specs that could be applied to all PCs.

"We want to make sure Longhorn platform capabilities will scale," explained another WinHEC presenter, Richard Russell, who is a developer in Microsoft's core Windows division. "Not just performance, but also high-definition video, extra memory and dual core."

In order to do so, a Longhorn PC will need a good BIOS that correctly implements the Advanced Configuration and Power Interface (ACPI) features for suspend, hibernate and resume, Russell said. It also should be able to be able to boot quickly, which new systems could (but do not have to) do by taking advantage of recently announced hybrid disk/nonvolatile RAM technology announced by some of Microsoft's partners, he said.

Russell did advise mobile PC makers to consider supporting 802.XX wireless; General Packet Radio Service (GPRS); Bluetooth; the various Tablet PC input technologies (including speech and touch, in addition to digital ink); ClearType, the hybrid flash/disk technology; and Longhorn's forthcoming Secure Startup capability, among other features.

For Longhorn PCs that are customized for "living-room scenarios," Russell suggested PC makers strongly consider optimizing around 64-bit, dual-core processors. He also said dual-channel memory; a minimum of 1 GB of memory; and a high-performance and capacity disk drive (averaging 3000 GB-plus)would all be nice to have.

"Longhorn will provide an absolutely fabulous gaming experience," Russell told WinHEC attendees. In order to be able to take the fullest advantage of Longhorn as a gaming platform, Russell suggested PC makers gravitate toward 64-bit dual-core processors, 1 GB of memory, 256 MB of graphics memory and advanced LDDM support.

Microsoft officials are advising OEMs to avail themselves of the new WinSAT tools that will be built into Longhorn to measure system performance in order to determine how well Longhorn will run on existing and new PCs. WinSAT also will run on Windows XP.