When I was around six years old, my parents got me the Golden Book Encyclopedia, this series of books for kids. Well, it was for my sisters and me. But I was the one who practically wore off the covers.
Three or four years later, Mom and Dad purchased the Encyclopedia Americana, ostensibly for the family, but I was clearly the greatest user by far. I may have read the whole thing, over time. Because the books became instantly dated, Americana sold these Annuals that would update the main books. My parents bought these as well, and I DID read the volumes practically cover to cover.
When I was living on my own, local supermarkets would often sell encyclopedias, one book a week. The first volume would be 99 cents, or maybe just a penny; subsequent books were three or four dollars each. I know I started buying these, because I ended up with a lot of A volumes; I knew more about aardwolves and Aachen than anyone should.
During my brief time in New York City, I was a telemarketer for about three months. I called people who had the World Book Encyclopedia already and ask them if they wanted to buy the Annual. I was rather good at selling these, as I recall.
Of course, now, most encyclopedias are available online, which makes them easier to keep up-to-date. Still, I still have a soft spot for those nearly uniform books that went from A clear down through Z.
That reminds me: I learned to spell the word encyclopedia from Jiminy Cricket on the Mickey Mouse Club.