The minimum recommended hardware for the beta includes a 1GHz processor, 1GB of system memory, 16GB of available disk space and support for DX9 graphics with 128MB of memory (to enable the Aero theme), Microsoft said. The recommendations may change for the final product, it said.

Microsoft isn't updating its official ship date for Windows 7, which is still early 2010, though some pundits expect it to ship in time for the busy back to school season later this year.

Among the new things in Windows 7 are an updated interface, including a redesigned task bar; tools to make home networking simpler; and a reworking of the User Account Control feature, which annoyed many Vista users with its constant prompts. It also aims to give better performance than Vista and supports a touch-screen interface, though few PCs are likely to use that feature at first.

Ballmer will announce that there are now 100 million active Vista users, and that an additional 80 million licenses have been sold but not yet activated, many to corporations. Few would call Vista a great success, however. Poor performance on all but the most powerful PCs, a lack of backwards compatibility and some annoying interface features have caused many to stick with Windows XP and await Windows 7.

TechARP.com, a tech enthusiast Web site, earlier this week that Microsoft will offer free or discounted Windows 7 upgrades to people who buy a Vista PC after July 1. That news, which Microsoft has not confirmed, is a sign that the company plans to ensure Windows 7 can run on a broad range of today's PC hardware, said Matt Rosoff, an analyst with Directions on Microsoft.