Microsoft Corp. said Tuesday that Windows 7, the next version of its computer operating software, will go on sale Oct. 22, in time to possibly give the slumping PC industry a lift in the holiday season.

Windows 7, which will replace the much-complained-about Windows Vista, will be available then on new PCs. Microsoft, the world's largest software maker, will also sell versions that people can install on existing PCs.

PC makers and resellers will offer free upgrades to Windows 7 for people who buy a new computer running the Home Premium, Business or Ultimate version of Windows Vista shortly before Windows 7 arrives. However, Microsoft did not say whether the upgrade program will begin in time for back-to-school shopping, another crucial period for the PC industry.

Industry analyst Roger Kay of Endpoint Technologies said it's reasonable to think Microsoft would offer upgrades two months in advance of Windows 7's launch — late August, in other words.

"The industry must be careful not to kill sales leading up to the introduction, and back-to-school is the first possibility of some relief in this market," Kay said.

Shares of Redmond, Wash.-based Microsoft closed unchanged at $21.40.