The first three options of the new operating system due out later this year are designed for machines running x86 processors; Windows RT is for devices built with ARM processors and that has been known until now as Windows on ARM (WOA).
Windows 8 can run on PCs and tablets powered by either 32- or 64-bit x86 processors, with plain Windows 8 suitable for consumers and including an upgraded version of Windows Explorer, Task Manager and better support for multiple screens.
BACKGROUND: Microsoft details 'Windows on ARM' program
The operating system can also switch languages quickly, except in the China edition, which will come with a local-language option only. That restriction may also apply to certain emerging markets, Microsoft says in its Windows Team Blog.
Windows 8 Pro is for businesses and will offer a wider range of features including PC management, virtualization, encryption and domain connectivity. Windows Media Center will be an add-on option.
Windows 8 Enterprise is a version of Windows 8 Pro for businesses with Software Assurance agreement with Microsoft. It includes tools for management and deployment, advanced security, support for virtualization and new mobility options that the company did not specify.
The Pro and Enterprise versions have a common set of features that are not included with the consumer Windows 8 that include BitLocker and BitLocker To Go Drive Encryption; booting from a virtual hard disk (VHD boot); a Hyper-V virtual client; a tool to make it easier for a machine to join, for example, a business domain from home (Domain Join); an encrypted file system; support for group policies; and a remote-desktop host.
Windows RT -- named after the new Windows runtime that is at the core of Windows 8's touchscreen capabilities -- will only come packaged with ARM hardware and maintenance and software options must come through Microsoft. The devices will be thin and lightweight, and will be miserly with power. They will also come preloaded with versions of Word, Excel, PowerPoint and OneNote.
Also unique to Windows RT will be preloaded native device encryption.
Pricing for all the new versions will be announced later, Microsoft says.