Microsoft Windows, the world’s most popular operating system, has come a long ways since its humble beginnings back in the mid-1980s. Today, the Windows OS is sold in four distinct but related forms. It powers millions of devices, from desktops to smartphones to tablets, all around the globe.

For the first decade or so of its existence, roughly 1985 to 1995, Windows was primarily a business operating system. Built on top of the earlier, text-based DOS OS, early versions of Windows brought the ease and flexibility of a graphical user interface, or GUI, to business professionals and government employees. While some home users also worked with Microsoft’s graphical OS during this time period, Apple’s Macintosh dominated the home, education, and creative markets.

The four currently produced versions of Windows are differentiated by the type of hardware they’re designed for: desktops/notebooks/tablets, smartphones, servers, and embedded devices such as point of sale terminals and ATMs.

Windows 8 is the Windows designed for standard computers and tablets. It is the version of Windows that the average person is likely most familiar with. Windows 8 is the latest in a long string of consumer-focused Microsoft operating systems, including Windows 95, Windows XP, and the frequently-maligned Windows Vista.

Windows 8 is a dramatic departure from past versions of the OS in that it features two completely different interfaces: a traditional desktop and a dynamic, tablet-esque “window pane” system. Like its predecessors, it includes support for multiple accounts, the largest library of software of any OS ever, and support for a nearly countless variety of hardware peripherals.

Microsoft’s line of Surface tablet/laptop hybrids, including the recently-released Surface 2 and Surface Pro, were created specifically to take advantage of everything Windows 8 offers. These exciting devices provide the casual convenience and touchscreen control options of a leading-edge tablet and, with the removable ultra-thin keyboard attached, the power and productivity of any normal laptop, as well. Many industry critics agree that the Surface really does, with the help of Windows 8, provide the best of both worlds.

The current Microsoft mobile OS is called Windows Phone. While Apple’s iOS and Google’s Android still split the lion’s share of the smartphone operating system market, Microsoft’s offering has garnered many positive reviews from industry publications and continues to creep up in popularity. Windows Phone features a unique graphical navigation system called Live Tiles, which is very similar to Windows 8′s tablet interface.

The two other versions of Windows currently available are Windows Server 2012 R2, for servers, and Windows Embedded 8, for embedded devices. Consumers are unlikely to encounter either of these operating systems in their day-to-day activities.