That's the good news. The bad news is that Longhorn is going toquite differently on those older systems. Computers with a 3GHz processor and 512MB of memory, for example, will get all of the bells and whistles including fancy graphics and the ability to handle multiple video streams. According to its early testing, Microsoft says that older PCs--probably those with as little as 128MB of memory--will be able to run Longhorn, but the OS may not look like it does on a newer, more powerful machine.
Many of these older machines that run Longhorn will have experiences that are "quite XP-like," said Richard Russell, a developer in Microsoft's Windows core operating system division.
There are at least fourfor the new Windows. Two of them--Aero and Aero Glass--will have new composited graphics, with the high-end Glass shell adding more three-dimensional effects and transitions. Another view, dubbed "To Go" is and other new consumer machines and has many of the same color schemes as Aero, but not the fancy graphics tricks. Finally, a classic mode will look much like XP or even Windows 2000.
But there are performance differences as well, with more-capable systems able to do more things in the new OS.
That represents a big philosophical shift for Microsoft. With past versions of Windows, including Windows XP, the operating system typically either ran on a machine in all its glory or didn't run at all.
"XP is XP is XP," Russell said. "Longhorn is much different. It will really scale."
Such variability poses a couple of challenges for the software giant. First, it has to educate businesses and consumers that being able to run Longhorn does not equate to being fully able to take advantage of all of its features. To that end, Microsoft is planning a new logo program for PCs that will separately identify machines that are optimized for Longhorn as opposed to those that are merely capable of loading the OS. The company also is working on a program that lets computer makers designate a PC as "Longhorn-ready."
A second challenge, which Microsoft said it is already planning to address, is putting the burden on the software to figure out what settings are most appropriate to the type of machine one has.
Russell said Microsoft will ensure that when people upgrade to Longhorn, settings are optimized for their machines, though users will still have the ability to change those settings.
"We don't want users to have to hunt and peck to find out if they can run (Aero) Glass," he said. Similarly, computer makers are encouraged to set defaults relative to the capabilities of their machines, though again, consumers can change those settings.
Directions on Microsoft analyst Michael Cherry believes Microsoft was too vague with its guidance on which hardware is needed for which features. Though the company offered some detail on processor and memory requirements, Cherry said, businesses still may not have enough information to know which graphics cards to look for on a new PC. He added that he was disappointed Microsoft doesn't have the "Longhorn-ready" guidelines already ironed out so that corporations can buy PCs now and know whether they will be good for the new OS.
"I don't understand why, at a hardware show, they aren't ready to give us the Longhorn-ready specification today," he said.