It was 1973 and Palo Alto Research Center (Xerox PARC) had just completed the Alto computer, the first commercial example of a computer GUI. While the screen orientation and lack of colors make it a little peculiar to the modern eye, it's clearly recognizable as a graphical interface, with a mouse and keyboard for interaction. While it took another seven years to be generally available to the public, in 1981, as the Xerox Star, it was clear that this was the beginning of something big:

This was a huge leap forward for the usability of computers—a welcome change from the standard interaction of text-mode computer screens. Not only does a graphical interface allow for more advanced functionality, it's also much easier to learn for a novice looking to get started. While the command-line interface remains popular with programmers and other experts, it's fair to say that, without the GUI, personal computers wouldn't have reached the popularity we all know: