SAN FRANCISCO - Microsoft will add its popular Outlook email program to more tablets running on a lightweight version of its Windows operating system as part of a free software update this year.

The Outlook 2013 app will be given to owners of Microsoft's Surface tablet and similar devices running Windows RT. That's a slimmed down version of Windows 8, a radical overhaul of the ubiquitous operating system used on most personal computers.

Microsoft Corp is preparing to modify Windows 8 in response to consumer complaints about the redesigned system released last October. The Redmond, Wash., company announced the addition of Outlook for Windows RT tablets Wednesday at a computer trade show in Taiwan.

A specific release date still hasn't been set for the upcoming update, called Windows 8.1. A preview version of Windows 8.1 will be available June 26 when Microsoft starts an annual programmers' conference in San Francisco.

Windows 8 includes touch-screen controls and displays applications in a mosaic of interactive tiles as part of an attempt to expand the system on to tablets. The operating system also remains compatible with keyboards, computer mice and programs created for traditional PCs.

The dual format has confused and frustrated some long-time users, contributing to lukewarm sales for devices running on Windows 8 and Windows RT.

Windows RT's omission of Outlook was among the grievances. Outlook's absence was magnified by Microsoft's inclusion of other popular programs, such as Word, Excel and PowerPoint, on the Surface tablet and other Windows RT devices. Unlike Windows 8 tablets, RT devices can run only programs specifically designed for it, so it hasn't been possible to buy Outlook separately.

Existing Window RT users will get Outlook for free as part of this year's Windows upgrade.

The Outlook announcement came as Microsoft showcased previously announced features of Windows 8.1 at the Computex show in Taiwan. Tami Reller, chief financial and marketing officer of the company's Windows Division, said the 8.1 update took into account input from consumers on the Windows 8 system.

"Windows 8.1 furthers the bold vision of Windows 8 by responding to customer feedback and adding new features and functionality that advance the touch experience and mobile computing's potential," Reller said.

Antoine Leblond, corporate vice president of Windows Program Management, demonstrated the upgraded system, which included enhancements in areas including platform personalization and search. Although Microsoft isn't restoring the traditional start button on the lower left side of the screen, it is restoring a logo in that spot and will let users add favorite applications, such as Word and Excel, to a horizontal tool bar while working in Window's traditional desktop mode.