The Macropædia was introduced in the 15th edition (1974) with 19 volumes having 4,207 articles. In the drastic reorganization of that edition in 1985, these articles were combined and condensed into 17 volumes with roughly 700 articles, ranging in length from 2-310 pages. The longest article, on the United States, resulted from the merging of the 50 articles on each state. The articles of the Macropædia are generally written by named contributors and have references, in contrast to the roughly 65,000 articles of the Micropædia that have no named contributor and no references. However, some parts of the Macropædia were written by the editorial staff of the Britannica; such editorial articles are identified by the initials "Ed."
ok, every 6th grader used to know this, but in fact Britannnica just went out of business: