The Web as you experience it — with pretty pictures, in a browser, with back and forward buttons — emerged exactly 20 years ago.

On Jan. 23, 1993, programmer Marc Andreessen released Mosaic, the Web browser credited with making the Internet accessible for the general public.

While not the first graphical Web browser, it was the most popular one of its time and still the model for today's browsers.

Before Mosaic, for example, images and text weren't able to display together. Each had its own window. There were no bookmarks; there wasn't even a back button.

Mosaic made all this possible — and for free. In fact, it's still available from Archive.org, or from the National Center for Supercomputing Applications (NCSA) at the University of Illinois Urbana-Champaign, where Andreessen, as a student, led the team that developed the software.

"NCSA Mosaic was available for free, and soon thousands of copies were being downloaded each month. It quickly moved beyond the research and education niche and became the first 'killer app,'" Danny Powell, NCSA's current executive director wrote to TechNewsDaily.

Ironically, to download the software from NCSA, you have to use a pre-Web technology called FTP. The university doesn't have a Web page where you can download the first Web browser.

NCSA states that the software was downloaded more than 5,000 times a month the peak of its popularity. By comparison, Google said in June 2012 that its Chrome browser has 310 million active users (Chrome was first released in 2008). Of course, the Web was far bigger by then.

"I don't think anyone foresaw the incredible impact Mosaic would have, but they knew it was something cool, something that would help people connect and explore and learn," Powell said.

Though Mosaic ushered in the modern Web, much of the credit goes to the Netscape browser, which debuted in 1994. That didn't deprive Andreessen of fame, however, since he was also the founder of Netscape. Andreessen now serves as principal of Andreessen-Horowitz, a company that invests in today's tech startups.