Print can lay claim to being the first mass medium. 20% of Americans don't (or can't) read. The average American reads .8 books a year.
It is traditionally been suggested that it first made an impact with the invention of Gutenberg's system of movable type in 1452. However, the earliest example of a printed book is the Diamond Sutra printed using movable clay type in China in 868CE. Though this is the earliest available example, it is thought this system was already well established when the Diamond Sutra was published. Gutenberg's innovation, made apparently without knowledge of the Chinese system, was to cast individual letter forms from metal.
Ratings are used to get statistics on popularity of programming. The ratings system used for TV is Nielsen, and the system for radio is Arbitron.
The press is called the "Fourth Estate." In the US, it is protected by the First Amendment. Print press is unrestricted, but TV and radio isn't. Radio stations and network broadcasters must have licenses. Cable networks aren't required to have licenses, so they can do whatever they want.
"On the Media" is an NPR show about media analysis. Audio and transcripts can be found at |http://www.wnyc.org/onthemedia/.