How were HTML forms interpreted in the early 90s?

Solution 1:

Before server side scripting (PHP, Ruby, node.js) there was server side programming.

One of the original interfaces between web servers and back-end processes was the Common Gateway Interface (CGI). It was introduced in the early 90s by the NCSA back-end team at the same time forms was introduced into HTML by Tim Berners-Lee (who was also at NCSA at the time). So forms was introduced at roughly the same time CGI was invented.

Initially a lot of people wrote CGI programs in C. I was one of those who had to do so as a homework assignment. Instead of a giant all-encompassing framework we wrote small C programs that read from stdin and print to stdout (we printed HTTP response, not just the HTML as per CGI spec). A website had lots of these small programs each doing one small thing and updated some database (sometimes that database was just a flat file).

Almost as soon as it was introduced people also started writing CGI scripts in Perl. So there was really no transition period between C programs and scripting languages. People simply stopped writing CGI scripts in C because it was faster to do so in scripting languages.

Solution 2:

Server side was actually always in the picture.

The Apache HTTP Server was available since 1995, and in 1996 it also had Perl support (which was used as a server-side programming language).

JavaScript was created in 1996 and Netscape was the first browser supported the client-side language (other browsers vendors implementations were based on the work that was done in Netscape).

In 1993 the Mosaic browser is released with support for images, nested lists and fill-out forms.

Basically - every HTTP server that could handle request and pass it to some application (no matter in what language that application is written in) is a server-side application. It can be written in scripting language (Perl/Python/PHP/Ruby), high-level language (Java/C#) and if you really want - even assembly. All you need to do is make sure you "follow the protocol".

Solution 3:

JavaScript wasn't so advance (hell Ajax wasn't even out yet). So it was pure server-side. Mostly CGI (being Perl) and PHP.

There was also Coldfusion but wasn't a popular favorite.

Eventually, at the end of 1999 and early 2000s ASP.NET (aspx) and JavaServer Pages (jsp) came out, although a lot of commercial sites used aspx and jsp for obvious reasons.

Note, Java applets also existed (mostly for rendering though) but had to be separately downloaded and supported by the browser.