So where is Surface Pro? Microsoft's much-hyped, business-friendly Windows 8 tablet is nowhere to be seen. The delay, according to industry sources, has thrown the company's tablet plans, and indeed much of its strategy around Windows 8, into disarray. The situation may even have contributed to former Windows chief Steven Sinofsky's sudden exit this week. Here's the background. Microsoft unveiled Surface earlier this year, revealing two versions. Surface RT, which runs Windows RT and shipped on Oct. 26, and Surface Pro, based on Windows 8 Professional. Windows RT is a Windows 8 derivative designed for consumer tablets. All Windows RT tablets are powered by ARM chips, and are designed to be light and long on battery life. The downside: They won't run regular Windows applications and are incompatible with many Microsoft security and management tools, including Active Directory.