MS-DOS (/ˌɛmˌɛsˈdɒs/ em-es-DOSS; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few operating systems attempting to be compatible with MS-DOS, are sometimes referred to as "DOS" (which is also the generic acronym for disk operating system). MS-DOS was the main operating system for IBM PC compatibles during the 1980s, from which point it was gradually superseded by operating systems offering a graphical user interface (GUI), in various generations of the graphical Microsoft Windows operating system.

This is the version that started it all. Windows 1.0 debuted in 1985 and was designed to be a GUI to be used in conjunction with MS-DOS. The use of Windows 1.0 as a GUI meant that MS-DOS users didn’t have to manually enter text commands just to complete basic tasks. Now, they could carry out tasks and browse their own files by just pointing and clicking on icons and menus. At the time of its release, Windows 1.0 cost $99 and introduced many computer users to drop-down menus, icons, and dialogue boxes. According to Microsoft, it also featured the ability to multitask applications and “transfer data between programs,” a first for a Microsoft OS.

It wasn’t long before Microsoft released a successor to its first GUI-enhanced OS. Just two years later, in 1987, the technology company released Windows 2.0. This version of Windows included such notable features as overlapping windows, resizable windows, keyboard shortcuts, and support for VGA graphics. The first Windows versions of Word and Excel also made their debut with Windows 2.0.

Microsoft’s next major milestone came with its release of Windows 3.0. This version of Windows is widely considered to be the start of Windows’ worldwide popularity as a desktop OS. Windows 3.0 came out in 1990 and offered 256 color support. More importantly, as PCMag notes, it featured “multitasking DOS programs,” which may have contributed to Windows’ surge in popularity. Another notable feature of Windows 3.0 is that it’s the version that saw the first appearance of the classic desktop game Solitaire.

Microsoft’s next major milestone came with its release of Windows 3.0. This version of Windows is widely considered to be the start of Windows’ worldwide popularity as a desktop OS. Windows 3.0 came out in 1990 and offered 256 color support. More importantly, as PCMag notes, it featured “multitasking DOS programs,” which may have contributed to Windows’ surge in popularity. Another notable feature of Windows 3.0 is that it’s the version that saw the first appearance of the classic desktop game Solitaire.

A mere two years later, another OS update appeared, upgrading Windows to one of its most iconic versions, 3.1. The decimal in its name may make it sound like it was just a minor update to 3.0, but it wasn’t. Instead, in 1992, Windows 3.1 delivered quite a few new and essential features, such as support for TrueType fonts, the ability to drag and drop icons, and support for OLE compound documents (documents that combine elements from different programs). Also, according to The Guardian, it’s also the first version of Windows to have been distributed via CD-ROM.

When you think of the most iconic version of Windows, you’re probably thinking of Windows 95. That’s because it was such a huge departure from previous versions of Windows and aesthetically-speaking, and it set the tone for what we’ve come to expect from the Windows OS. As its name suggests, Windows 95 came out in 1995. It was the first 32-bit version of Windows (previous versions had been 16-bit), and it brought quite a few new features that ended up becoming historic additions. These include the taskbar, the Start menu, long file names, and plug-and-play capabilities (in which peripheral devices only needed to be connected to a PC in order to work properly). Windows 95 also saw the introduction of Microsoft’s web browser, Internet Explorer.

Another significant feature? Though Windows 95 still worked in conjunction with MS-DOS, as PCMag notes, unlike its predecessor, Windows 95 didn’t have to have to wait for the PC to boot into DOS first. This version marked the first time Windows was allowed to boot directly.

This is yet another version of Windows with a name that indicates the year it was released. If Windows 95 (eventually) brought us Internet Explorer, then Windows 98 strengthened the web browser’s grip on Microsoft’s OS. Indeed, this version of Windows not only brought us Internet Explorer 4.01, but it also delivered a slew of other internet-based programs and tools, such as Outlook Express, Microsoft Chat, and the Web Publishing Wizard.

Windows 98 also came with increased support for USB devices and Macromedia players (Shockwave and Flash).