The Xerox Alto, developed at PARC in the early 1970s, is widely regarded as the first personal computer. It featured a graphical user interface (GUI) with icons, windows, and a mouse, which made it much easier to use than previous text-based systems. The Alto also introduced the concept of object-oriented programming, which has since become a fundamental principle of software development.

PARC's work on personal computers had a profound impact on the industry. The ideas developed at PARC were later incorporated into the Apple Lisa and Macintosh computers, which helped to popularize the use of personal computers. PARC's contributions also laid the foundation for the modern graphical user interface, which is now used on most computers and mobile devices.

Here are some specific ways in which PARC's work on personal computers was revolutionary:

* The graphical user interface (GUI): The GUI made it much easier for users to interact with computers by using icons, windows, and a mouse instead of text-based commands. This was a major breakthrough that made computers more accessible to a wider range of people.

* Object-oriented programming (OOP): OOP is a programming paradigm that emphasizes the use of "objects" that contain both data and methods. This makes it easier to develop and maintain complex software programs. OOP has since become one of the most popular programming paradigms in the world.

* The mouse: The mouse is a pointing device that allows users to interact with computers by moving a cursor on the screen. This was another major breakthrough that made computers more user-friendly. The mouse has since become a standard feature on most computers.

PARC's work on personal computers was truly revolutionary and has had a lasting impact on the industry. The ideas developed at PARC have helped to make computers more accessible, easier to use, and more powerful.