A white paper published this morning by hardware analysis firm iSuppli, based on its studies of Microsoft Windows Vista running on multiple grades of computer hardware, has concluded that the software publisher's stated minimum requirements for the system -- which include an 800 MHz processor, 512 MB of RAM, and a 35 GB hard drive -- may not be nearly enough.

"Despite Microsoft's claims that Vista can run on such trailing-edge systems," writes Matthew Wilkins, principal analyst for compute platforms research, "iSuppli believes the reality is quite different."

The reason for what many consumers will consider expensive upgrades isn't what you might think at first. While a great deal of extra processing power, especially in the graphics department, is necessary for Vista to run the "full experience" of its Aero operating environment -- including, for instance, the ability to flip application windows around in full 3D rendering -- Wilkins points out that Aero is merely an option, that it isn't really a necessary one, and that it can be turned off.

No, the reason is the one that should be more obvious, were it not obstructed by the superficial ones: It's just Vista, and it needs more processing power just to be Vista.

Besides the CPU, the biggest factor impacting the overall cost of a Vista-capable system will be memory, iSuppli says, not graphics. For system builders and OEMs producing PCs today, the firm's charts make clear, they'll build Windows XP-capable systems with the same CPU as for their Vista-capable systems, so buyers of new computers this holiday season won't find new systems with XP pre-installed that are incapable of running Vista.

Wilkins pointed out some reports may be over-dramatizing the notion that older PCs can't run Vista, saying that while Microsoft's stated requirements may be unrealistically low, even older PCs today meet or beat those specifications.

Memory will drive up component costs, however, and could be principally to blame for price differences that users will see between XP systems that are "Vista-ready" and those that are "Vista-capable" (Microsoft has asserted their differences).

A 2 GB comfort zone for desktop DRAM -- up from the 1 GB zone of realism for XP -- would naturally double suppliers' costs for memory per unit, and thus drive up their total component costs per unit up, iSuppli calculates, by as much as 20%. Factor in the resale margin, and consumers could be paying one-fourth more for a system intended to run Vista.

ISuppli's contentions run completely contrary to those recently made by Acer Senior Vice President James Wong. He claims that Microsoft has been engaged in a campaign to compel users to purchase more expensive computers than they really need, by virtue of the same fact iSuppli's Wilkins believes is inconsequential: The full "Aero" experience will not be appreciated by users whose systems will only run Vista Basic.

Earlier this year, there may have been some evidence to support Wong's claims. At that time, it was reported that Microsoft and graphics card producer ATI were actively developing a campaign based on Microsoft's new Windows System Performance Ranking (WSPR), to divide the consumer PC market into five tiers of performance rather than just two. The middle and upper tiers of this system would have been the more "preferred" levels, and they would have mandated much higher-level performance specifications than hardware analysts such as iSuppli believed were being sold to everyday consumers at that time.

As it turned out, Microsoft adopted quite the opposite approach, perhaps after evaluating public response to news of that policy under consideration.

While iSuppli projects, under ordinary circumstances, consumers may pay 20% plus margins more for Vista-capable PCs than for XP-capable ones, it's December, so these are not ordinary circumstances.

A check of TigerDirect.com this morning revealed HP systems with a 3.06 GHz single-core Pentium 4 524 processor, with integrated video, 160 GB hard drive and 512 MB of DRAM -- well within the tolerance limits for Windows XP -- is selling for $499.99, less a $200 holiday rebate.

Meanwhile, a Systemax system from the same vendor configured with a 3 GHz Pentium 4 531 processor, 160 GB hard drive, and 2 GB of DRAM -- as iSuppli suggested for Windows Vista -- sells for $829.98, and is without a rebate offer. So as retailers such as TigerDirect shed their XP baseline systems, the spread right now (counting rebates) appears not to be 25%, but as much as 64%.