Peter Klein told the audience at a Goldman Sachs technology conference in San Francisco that Microsoft gave developers a preview of the new operating system in fall and will add consumers to the audience with a so-called “consumer release” later this month. The staged introduction will allow users to “absorb what is new in Windows 8 and why it really builds on traditional value,” Mr. Klein said. Windows 8, which isn’t expected to go into commercial release until late this year, is designed to position Microsoft in the fast-growing tablet market dominated by Apple Inc.’s iPad and devices that run Google Inc.’s Android software. Windows 8 is critical to Microsoft’s mobile future, and insiders say it represents the most dramatic overhaul of the operating system since the release of Windows 95, 16 years ago.