Phillip Greenspun:

Publishing from Gutenberg (1455) through 1990

1. The pre-1990 commercial publishing world supported two lengths of manuscript:
   the five-page magazine article, serving as filler among the ads

2. the book, with a minimum of 200 pages

Suppose that an idea merited 20 pages, no more and no less? A handful of long-copy magazines, such as the old New Yorker would print 20-page essays, but an author who wished his or her work to be distributed would generally be forced to cut it down to a meaningless 5-page magazine piece or add 180 pages of filler until it reached the minimum size to fit into the book distribution system.