However, the operating system also plays a major role in the cost differences, said IDC, with XP more expensive to support in every category the research company surveyed.
Organizations reported that they spent 82% less time managing patches on Windows 7 systems than they did on Windows XP, 90% less time mitigating malware, and 84% less help desk time.
Benefits were also striking for Windows 7 users' productivity compared to XP. Windows 7 users wasted 94% less time rebooting their computers and lost 90% less time due to malware attacks.
On the IT side, the savings of Windows 7 mount dramatically, IDC said.
"IT activities account for 11.3 hours of time spent per PC per year when using Windows XP," the research group said. "Shops that have moved to Windows 7...spend 2.3 hours per PC per year on maintaining those systems."
IDC did the math, and concluded that for every 230 PCs running Windows 7 rather than XP, an organization could shift one full-time IT person to other work. Or conceivably do without him or her entirely.
The Microsoft-commissioned report also painted a rosy return-on-investment (ROI) picture for companies who do ditch XP for Windows 7. By IDC's calculations, the acquisition of a new PC -- one where Windows 7 is retained as the OS rather than being downgraded to XP -- pays for itself in one year and generates almost $1,000 more in savings from reduced IT costs and worker downtime over a three-year span.
"The migration from Windows XP to Windows 7 yields a 137% return on investment over a three-year period," claimed IDC.
Windows XP have a shortening upgrade window -- no pun intended -- and not only because of the April 2014 end to all support. Microsoft is expected to launch Windows 8 this fall, a time when most new PCs will then also be pre-loaded with the OS by computer makers, or OEMs.
That will not immediately strike Windows 7 from the rolls, but it does start a couple of clocks ticking: OEMs can continue to sell Windows 7-powered PCs as long as two years after Windows 8's launch, but the older operating system will disappear from most retail outlets one year earlier, or in the fall of 2013.
Organizations that have Software Assurance (SA) agreements -- the Microsoft-sold software insurance policy that lets firms upgrade to every new version of a specific product released during the life of the deal -- can downgrade any Windows 8 PC to Windows 7. But SA is almost exclusively an enterprise program.