Microsoft has announced, through their blog, that its next iteration of Windows, Windows 8 will only have three versions. Out of the three, only two will be available for consumers while one will only be available to partners and will be pre-installed.
For consumers, there is Windows 8 and Windows 8 Pro. Windows 8 will replace those that are happy with Windows 7 Starter, Home Basic, and Home Premium. Most of the features consumer need will be in Windows 8. You also get Internet Explorer 10, a new Task Manager, and better multi-monitor support aside from the new Metro Interface.
For the enthusiasts and businesses, Windows 8 Pro adds additional features such as business-class encryption, virtualization, and business-class network features.
It still isn’t known whether there is a separate installer for 32-bit or 64-bit editions but from the Developer and Consumer Preview, you will still have different installers for either version.
The last version really doesn’t matter to consumers in terms of installing to a new hardware. Windows RT will be pre-installed on devices using the ARM processor such as on PCs and Tablets. ARM processors are better known as the chipsets that are in the latest mobile devices (smartphones and tablets) including those that are running Android, iOS, Windows Phone, and even Blackberry OS. Devices running Windows RT are known as Windows on ARM devices or WOA.
The Windows Blog has a partial chart on the different features for each version of Windows 8.
Source: The Windows Blog