
I just love stuff like this. Have you ever wondered why books (and, by extension, e-reading devices) are the size that they are?
For some historical perspective regarding that question, courtesy of Wired: “The Hidden Link Between E-Readers and Sheep (It’s Not What You Think)” —
“It’s easy to figure out why e-readers and tablets are the size that they are: They’re all about the size of paperback books, whether trade (iPad) or mass-market (the Kindle 3). Some oversized models, like the Kindle DX, are closer to big hardcovers. But why are books the size that they are? It turns out it’s because of sheep. Sheepskin, to be exact.”
Parchment, by virtue of its availability and durability, has a long history with book-making (here’s a nifty BBC video on how parchment was made, for those that are interested). Since 1 sheep >>>>> 1 sheet of parchment, a sheet of parchment was thus the size of a sheep. Book-size naming conventions derive from the number of folds of said sheep skin:

“So think about that the next time you hear a tech pundit clamoring for a 7-inch iPad “mini,” a “paperback” e-reader, or an E Ink broadsheet newspaper that can be read and then thrown away. Some monk scraped all the hair and fat off a dead sheep’s skin so you could enjoy your finery.”
Interesting, no? I’m still wondering, from the title of that Wired post — what were we supposed to be thinking?
For more background context, be sure not to miss the excellent post from GotMedieval.com (“Why are books so big?”), beginning with a question about the size of medieval books, and leading to our question of interest about the origins of the size of books, in general —
“The question then becomes, I guess, why were medieval books the size they were? And the answer to that is simple: medieval books were the size they were because medieval sheep were the size they were. Remember, paper wasn’t the original medium for page-creation. Medieval books were constructed of parchment, which is a fancy word for sheep or goat skin (and primarily sheep skin, because there were a lot more of them around) …”