Microsoft Windows 8 is the newest member of the Windows operating system line and features major user interface changes over its predecessors.

Windows 8 Release Date
Windows 8 was released to manufacturing on August 1, 2012 and was made available to the public on October 26, 2012.

Windows 8 is preceded by Windows 7 and is currently the most recent version of Windows available.
Windows 8 will eventually have a successor as well, likely Windows 9.

Windows 8 Editions

Four editions of Windows 8 are available:
Windows 8.1 Pro
Windows 8.1
Windows 8.1 Enterprise
Windows RT 8.1

Windows 8.1 Pro and Windows 8.1 are the only two editions sold directly to the consumer and are available via download or boxed copy. Windows 8.1 Enterprise is the edition intended for large organizations.

All three editions of Windows 8 already mentioned will be available in either 32-bit or 64-bit versions.
A Windows 8.1 Pro Pack is also available [Buy: Microsoft | Other] which will upgrade Windows 8.1 (the standard version) to Windows 8.1 Pro.

Important: The most recent version of Windows 8, currently Windows 8.1, tends to be what is sold on disc and via download now that Windows 8.1 is released. If you already have Windows 8, you can update to Windows 8.1 for free via the Windows Store.

Windows RT, previously known as Windows on ARM or WOA, is an edition of Windows 8 made specifically for ARM devices. Windows RT is only available to hardware makers for preinstallation and only runs the software included with it or downloaded from the Windows Store.

Windows 8 Updates

Windows 8.1 was the first major update to Windows 8 and was made available to the public on October 17, 2013. Windows 8.1 Update was the second and currently the most recent update. Both updates are free and bring feature changes, as well as fixes, to the operating system.
See How to Update to Windows 8.1 for a complete tutorial on the process.
See Latest Microsoft Windows Updates & Service Packs for more information about major Windows 8 updates, as well as service packs for previous version of Windows.

Note: There is no service pack available for Windows 8, nor will there be one. Instead of releasing service packs for Windows 8, as in Windows 8 SP1 or Windows 8 SP2, Microsoft releases large, regular updates to Windows 8.

Windows 8 Licenses
Any version of Windows 8.1 you buy from Microsoft or another retailer, via a download or on a disc, will have a standard retail license. This means that you can install it on your own computer on an empty drive, in a virtual machine, or over any other version of Windows or other operating system, as in a clean install.
Two additional licenses also exist: the System Builder license and the OEM license.

The Windows 8.1 System Builder license can be used in similar ways to the standard retail license, but it must be installed on a computer intended for resale.
Any copy of Windows 8.1 Pro, Windows 8.1 (standard), or Windows RT 8.1 that comes preinstalled on a computer comes with an OEM license. An OEM Windows 8.1 license restricts use of the operating system to the computer on which it was installed by the computer manufacturer.

Note: Prior to the Windows 8.1 update, Windows 8 licenses were much more confusing, with special upgrade licenses with strict installation rules.
Beginning with Windows 8.1, these types of licenses no longer exist.

Windows 8 Minimum System Requirements

Windows 8 requires the following hardware, at a minimum:
CPU: 1 GHz with NX, PAE, and SSE2 support (CMPXCHG16b, PrefetchW, and LAHF/SAHF support for 64-bit versions)
RAM: 1 GB (2 GB for 64-bit versions)

Hard Drive: 16 GB free space (20 GB free for 64-bit versions)

Graphics: A GPU that supports a least DirectX 9 with a WDDM driver
Your optical drive will need to support DVD discs if you plan on installing Windows 8 using DVD media.
There are also several additional hardware requirements for Windows 8 when installed on a tablet.

Windows 8 Hardware Limitations
32-bit versions of Windows 8 support up to 4 GB of RAM. The 64-bit version of Windows 8 Pro supports up to 512 GB while the 64-bit version of Windows 8 (standard) supports up to 128 GB.

Windows 8 Pro supports a maximum of 2 physical CPUs and the standard version of Windows 8 just one. In total, up to 32 logical processors are supported in 32-bit versions of Windows 8, while up to 256 logical processors are supported in 64-bit versions.

No hardware limitations were changed in the Windows 8.1 update.

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