A: There will be four versions of Windows 8. However, only two of them will be available for purchase through retail channels: Windows 8 and Windows 8 Pro.

The four versions and their features are shown below, although other features might be added at the final release. Windows RT is the final name for the version of Windows that will run on ARM devices. It focuses on applications that leverage the WinRT application framework.

Feature name Windows 8 Windows 8 Pro Windows 8 Enterprise Windows RT
Upgrades from Windows 7 Starter, Home Basic, Home Premium x x  

Upgrades from Windows 7 Professional, 
Ultimate

x  
Start screen, Semantic Zoom, Live Tiles x x x x
Windows Store x x x x
Apps (Mail, Calendar, People, Messaging, Photos, SkyDrive,
Reader, Music, Video)
x x x x
Microsoft Office (Word, Excel,
PowerPoint, OneNote)
  x
Internet Explorer 10 x x x x
Device encryption
  x
Connected standby x x x x
Microsoft account x x x x
Desktop x x x x
Installation of x86/64 and desktop software x x x
Updated Windows Explorer x x x x
Windows Defender x x x x
SmartScreen x x x x
Windows Update x x x x
Enhanced Task Manager x x x x
Switch languages on the fly (Language Packs) x x x x
Better multiple monitor support x x x x
Storage Spaces x x x
Windows Media Player x x x
Exchange ActiveSync x x x x
File history x x x x
ISO / VHD mount x x x x
Mobile broadband features x x x x
Picture password x x x x
Play To experience
x x x x
Remote Desktop (client) x x x x
Reset and refresh your PC x x x x
Snap x x x x
Touch and Thumb keyboard x x x x
Trusted boot x x x x
VPN client x x x x
BitLocker and BitLocker To Go x x
Boot from VHD x x
Client Hyper-V x x
Domain Join x x
Encrypting File System x x
Group Policy x x
Remote Desktop (host) x x
BranchCache   x  
DirectAccess   x  
AppLocker   x  
Windows To Go   x  
Windows 8 App Deployment side-load   x  
VDI enhancements   x  

Windows RT will only be available preinstalled on ARM tablets and devices, while Windows 8 Enterprise Edition will only be available to customers with enterprise agreements with Microsoft.

Microsoft has a detailed blog entry on Windows 8 Enterprise that explains it more. The Microsoft Desktop Optimization Pack and Windows Intune remain additional components.

 See more FAQs about Windows, System Center, virtualization, Windows 8, and all things IT at John Savill's FAQs.