The most common form of adult content is a categorized list (more often it's a table) of small pictures (called "thumbnails") linked to galleries.
These sites are called a Thumbnail gallery post (TGP).
This type of distribution was generally free (apart from fees for Internet access), and provided a great deal of anonymity.
A 2015 study finds "a big jump" in pornography viewing over the past few decades, with the largest increase occurring between people born in the 1970s and those born in the 1980s.
While the study's authors note this increase is "smaller than conventional wisdom might predict," it's still quite significant.
One recent entry into the free pornography website market are Thumbnail gallery post sites.
These are free websites that post links to commercial sites, providing a sampling of the commercial site in the form of thumbnail images, or in the form of Free Hosted Galleries—samplings of full-sized content provided and hosted by the commercial sites to promote their site.
Around this time frame, pornography was also distributed via pornographic Bulletin Board Systems such as Rusty n Edie's.
These BBSes could charge users for access, leading to the first commercial online pornography.
The invention of the World Wide Web spurred both commercial and non-commercial distribution of pornography.
The rise of pornography websites offering photos, video clips and streaming media including live webcam access allowed greater access to pornography.
Children born in the 1980s onward are also the first to grow up in a world where they have access to the Internet beginning in their teenage years, and this early exposure and access to Internet pornography may be the primary driver of the increase.
The sex and tech conference series Arse Elektronika dedicated their 2007 conference to what they call pr0nnovation.
One of the early Gopher/FTP sites was at tudelft and was called the Digital Archive on the 17th Floor (List of websites founded before 1995).