The easy upgrades from Windows XP are done, say migration experts, who predict that a sizable number of large enterprises will still be running the aged operating system after Microsoft stops supporting it.
Microsoft plans to retire Windows XP from all support, including security patches for the public, on April 8, 2014.
"Our studies have shown that large enterprises have made the least progress in migrating from Windows XP to Windows 7, with 64% yet to complete their migrations," said Betty Junod, director of desktop product marketing at virtualization vendor VMware.
Slightly more than half of midsize organizations have not finished migrating, she added.
Browsium, whose Ion tool lets users run older versions of Internet Explorer inside newer editions of Microsoft's browser, agreed. "What's left are the difficult and expensive migrations facing the largest of enterprises," said Gary Schare, the company's president and COO.
"Our typical customer is a big, old organization -- banks, healthcare, government," Schare said. "And every single one of them is stuck on its migration" from XP to Windows 7.
Data published by Web metrics vendor Net Applications can be used to roughly plot XP's future usage share. If the average decline of the last 12 months holds, XP will still be the operating system in use on 33% of all PCs running Windows at the end of April 2014.
As for the corporate market, Microsoft CFO Peter Klein said in January that 60% of all enterprise PCs were running Windows 7. Since few businesses adopted Windows Vista and even fewer have jumped on Windows 8, almost all of the remaining 40% are likely running Windows XP.
If Microsoft stops support on schedule, around 450 million PCs -- by Computerworld's calculation using Net Applications data -- will be running without the safety net of Microsoft's patches.
This version of this story was originally published in Computerworld's print edition. It was adapted from an article that appeared earlier on Computerworld.com.