NCSA Mosaic — A Web Browser That Showed Images

NCSA Mosaic was the web browser released in 1993 by the National Center for Supercomputing Applications (NCSA) at the University of Illinois. The machinery of the Web had been built at CERN by Tim Berners-Lee in 1989–1990 (see the Web proposal). What Mosaic changed was what the Web looked like. Text and pictures on the same page, links followed with a mouse: this was where the basic shape of today's browser was first seen by large numbers of people outside research.

Four Months in 1993

Mosaic came out in public, on the Web developers' mailing list www-talk, in releases spaced roughly two weeks apart.

In the 0.5 announcement Andreessen said he wanted feedback on design and functionality more than bug reports for now, and expected new releases every seven to fourteen days until 1.0. The www-talk archive does show 0.6, 0.7 and 0.8 following in turn. NCSA's own history quotes Berners-Lee, in his book Weaving the Web, crediting Andreessen with listening closely to criticism and caring above all that people actually used the browser.

The IMG Proposal

Mosaic's signature feature is almost fully described in a single message of 25 February 1993. Andreessen proposed an IMG tag with no closing tag and one required argument, SRC, a URL. The browser would fetch the image over the network and show it "embedded in the text at the point of the tag's occurrence." Placed inside a link, the image became an icon that could be clicked like text.

He left the choice of image formats to each browser; X Mosaic would show a default bitmap when it could not read one. And he added that the feature was already working in X Mosaic and that NCSA would be using it internally at least. The order was telling: a working implementation first, the proposal for a standard second.

Berners-Lee, Dave Raggett and Guido van Rossum were among those who replied in the thread. <img> stuck, and it is still on practically every page on the Web.

Not the First Graphical Browser

Mosaic is sometimes called "the first graphical browser." It was not. CERN's history of the Web notes that several browsers, mostly for the X Window System, were written before it, naming MIDAS by Tony Johnson of SLAC, Viola by Pei Wei, and Erwise by students at the Helsinki University of Technology.

NCSA's own account makes a narrower claim. Earlier browsers were troublesome to get running, while Mosaic was much easier, which NCSA credits largely to Eric Bina's programming. And Mosaic was, in NCSA's words, "the first published browser that automatically displayed pictures along with text." Pages that mixed images and prose like a magazine were, in NCSA's view, what later drove the Web's growth.

What Was in 1.0

The announcement of 21 April 1993 read less like a launch than a changelog. It listed a workaround for Sun machines that crashed when looking up their own hostname, dialog boxes that now closed along with their window, sturdier GIF-reading code, a fix for an infinite loop triggered by an extra space in an IMG tag, and better support for Solaris, HP-UX and NeXT. It was signed "Marc & Eric." This was still a tool made by two developers at a university research centre.

At this point Mosaic ran only on Unix workstations. Reaching ordinary users required the Windows and Mac versions that came later in the year. CERN writes that the move to PCs and Macintoshes had an immediate impact on the spread of the Web.

The Spread in Numbers

By CERN's count, there were over 500 known web servers by late 1993, and the Web accounted for 1% of internet traffic. By the end of 1994 there were 10,000 servers, 2,000 of them commercial, and 10 million users.

In December 1993 Mosaic made the front of the New York Times business section. According to NCSA, more than 5,000 copies a month were being downloaded by then, and the article reported that Mosaic's supporters were calling it the first "killer app" of network computing.

What Happened Next

Most of the people who built Mosaic soon left NCSA. In April 1994 Andreessen co-founded Mosaic Communications with Jim Clark, founder of Silicon Graphics, joined by five other former students and staff of the university who had worked on NCSA Mosaic's design and development. Concerns raised by the University of Illinois led to a change of name to Netscape Communications that November; that story is told in the article on Netscape Navigator.

The other line of descent ran through licensing. Spyglass licensed Mosaic's technology and trademarks from NCSA, but according to Eric Sink, one of its developers, Spyglass used none of the NCSA code and wrote its Windows, Mac and Unix browsers from scratch. Microsoft licensed Spyglass Mosaic to build Internet Explorer, and Sink recalls IE 2.0 as Spyglass Mosaic without many changes.

Development of NCSA Mosaic itself ended with version 3.0 in January 1997. It lived for barely four years. But pages with pictures in them, images you could click, and a browser you could install and simply use all start here.