At some point along the way webmasters around the net realized that HTML (1) was too limited to do many of the things that they wanted to accomplish.
How could a webmaster display the current time and date on every page accessed by a client? How could she collect information about clients who were accessing her web site? How could she create a web site that was more than just an information warehouse, but a meaningful and dynamic conversation?
Certainly, HTML was great for distributing "pre-prepared" web pages on request. A client would use a web browser to contact a web server and use HTTP to ask the web server for a specific HTML document. (2) The web server would then send the requested document back to the web browser which in turn, would display the document as defined by the HTML to the client.
Pretty nifty really, and far superior to older technologies like gopher and ftp. However, the interaction between the client and the server was still extremely trivial. The server could only provide HTML documents that had been specially encoded by a webmaster, and that had been placed in certain publicly-accessible directories. The interaction between web browser and web server was pretty mind numbingly simplistic and the coolness of surfing through hyperlinks quickly became droll.
HTML fell short for anything truly "dynamic".
For example, to put the current date on every page using only HTML would require a webmaster to manually edit every file, every day. As you can imagine, this got tiring very quickly for sites with more than 5 pages. Webmasters needed a way to have HTML pages created and modified "on-the-fly," with information that could change weekly, daily, by the second, or for each and every request. And they needed those pages to be modified automatically, without their constant oversight.
As it so happens, the hardware that web server software runs on typically has quite a few resources that can be utilized to help solve these problems. Not only do servers have processing power to spare, they also have a battery of applications (such as e-mail, database manipulation, or calendaring) already installed and ripe for utilization.
And thus was born CGI (Common Gateway Interface). (3)
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