Systems running Vista, XP, or older versions of Windows won't be able to run the software, meaning that more than half of all computers currently running Windows would need an upgrade to run Office 2013.
Microsoft earlier this week posted the system requirements for Office 2013 Customer Preview on one of its support sites. Compatible operating systems are limited to Windows 7, Windows 8, Windows Server 2008 R2, or Windows Server 2012.
A spokesperson confirmed the requirements are applicable to the final version of Office 2013.
Systems will also need a processor that can run at a minimum of 1 GHz, and have 1 GB of RAM for 32-bit systems or 2 GB for 64-bit hardware. Also, 3 GB of available hard disk space is required, as is a DirectX 10-compatible graphics card for users who want hardware acceleration.
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The most noteworthy requirement is that PC systems run either Windows 7 or Windows 8. Windows XP is more than a decade old, but by some estimates it's still used on the majority of enterprise PCs. Microsoft has said it will end all support for XP in 2014. Vista is only five years old, though it's got minimal market share.
Microsoft is clearly hoping that Office 2013 provides incentive for users running older versions of Windows to upgrade. For most businesses, that means going from XP to Windows 7. Many companies have yet to make the jump to Office 2010.
"Most organizations are still working on Windows 7 and Office 2010 deployments," said Gartner analyst Michael Silver. "I don't think they'll be spending too much time worrying about Office 2013 until late 2013 or early 2014."
According to data published by market watcher Net Applications, 51% of PCs are still running Windows XP or Vista, while only 42% are running Windows 7. Windows 8 is expected to be released in October.
At the launch event, Ballmer called Office 2013 "the most ambitious release of Microsoft Office that we've ever done." He emphasized its touch capabilities, and the fact that it's integrated with cloud services like SkyDrive and Office 365.
Microsoft has yet to reveal a specific launch date or pricing details for Office 2013.