While Windows is by no means the only GUI-based operating system, it was and is the most widespread operating system in use. The mouse and graphical user interface, or GUI, opened up a world of opportunity for the less savvy computer user, numerous in the pre-internet era. The development of Windows brought about a fundamental change in how we interact with these computers and lowered the learning curve to using one right out of the box. Most functions were text-only and programs often needed some basic understanding of DOS programming to be useful to the average user.
DOS was a capable operating system, but its structure was text-based and required users to know at least some basics to run it.
In the early 1980s, Bill Gates and his software company, Microsoft, already held a huge market share of the operating systems run on desktop computers, MS-DOS, often shortened to DOS.