The Microsoft Windows operating system is available for purchase directly through Microsoft's web site, and can also be purchased at other retailers, such as Amazon.com and Newegg.com. Different retailers offer various versions of Windows for purchase, and not all versions of Windows may be available from all retailers.
Microsoft's online store only sells the Windows 10 operating system. Third party retailers like Amazon.com, Newegg.com and others offer older versions of the Windows operating system. Some versions are sold directly by the retailer, but others may be sold by third-party sellers on these websites.
Windows 10 is available as a direct download or on a USB drive. Older versions of Windows are generally only available on CD, as this is the method Microsoft used to distribute them during their original releases. When purchasing Microsoft operating systems from third party retailers, make sure that the retailer is reputable. Some resellers may not include authentic product keys with the copies of Windows that are sold. These product keys are required to activate Windows operating systems once they are installed on a computer.
Different versions of Windows have different hardware requirements. Before buying a Windows operating system, a user should check the requirements to ensure his computer supports running Windows.