I was talking to Chris over at Aspiring Lich about B/X Dungeons & Dragons (Moldvay/Cook) the other day and the topic of spell books came up. Mainly, how big is a B/X spell book and just how many spells can you put in one? Although there are no real specifications on the dimensions of a spell book, a closer read of both the Basic and Expert rules revealed some interesting information.
I have to admit that I had intended to do an in depth, page by page analysis of whatever I could find pertaining to spell books and offer up an answer for this. I took notes, read through the rule books and had my plan of attack all laid out. But, it got to being late so I set my notes aside and headed to bed. Of course, just before you nod off, it seems your mind is flooded with all kinds of good ideas and inspirations. I came to realize that all of my 'research' was totally unnecessary.
B/X is not a system that needs extensive changes, heck, it doesn't need any changes in my opinion. That is the beauty of those two books. The perfectly encapsulated pages contain everything you need to have a fun game without sweating over small details. So, in the morning after some coffee, the notes went out with the trash. But, this still didn't answer the question about the size of spell books...
Now, the rules do give some hints about it. It is mentioned that a magic user or elfs spell book is 'large' (page B16). There is mention about the price of replacing a book if it is lost or destroyed (page X11). A cost of 1000gp per spell level is needed and then a set amount of time spent studying and rewriting everything. What a bargain! Page X11 says that a spell book will always have the amount of spells equal to the number and level of spells that a magic user or elf can use in a day. So it stands to reason that a spell book is big enough to hold 14 elf spells and 22 magic user spells. Since this is the most they are able to cast (at 10th and 14th levels respectively), the book should have enough pages to hold them all. Easy-peasy, right?
Lets say you are playing a 1st level elf. At some point before your adventuring career begins, you are given a large, well made tome with many blank pages. Within is inscribed the one spell you can cast. You are instructed that it is important not to lose this or let it be destroyed. Also, when you have earned enough experience and advance to a higher level, come back to the mages guild and talk with your mentor to gain another spell. Don't worry, the new spell will fit, in fact all of your spells will fit. Since B/X rules don’t mention anything about copying scrolls into spell books, you wont have to worry about this taking up more space either.
Does this mean a spell caster will have only one book? Of course not. Let us assume that a magic user has reached 15th level, is maxed out in his current spell book and somehow manages to get another spell. Perhaps he has researched a totally new one (page X51). Or, maybe the magic users guild are so impressed by an accomplished deed that they bestow a super-secret spell previously unknown to your average magic user. What if the character spends a lot of time researching at the guilds libraries and the Dungeon Master lets them ‘redo’ their spell books with all different spells!
Have the character pay the cost of getting a new book and re-scribe their spells until its full again. The same goes for a spell caster who wants a backup book to take with them on an adventure. We know from examples in the Expert rules that spell books are needed to relearn your spells, so a character can travel with them. In fact, on page X19 it describes an equipment list for an adventuring party and 'spell books' are mentioned.
But what does all this blather mean you say? How can I run a game without knowing the EXACT size of a spell book and its weight? I say you don't need it. Keeping things simple and light is what B/X is all about. Sure, you can house-rule the game until you end up with a Frankenstein's Monster set of rules, but you would be missing the point and the beauty of B/X. It wasn't designed with all the answers, nor are they necessary. Moldvay, Cook, Marsh...They got this system right in my opinion. I don't think there is anything else to add.
In the end, a spell book is large enough to hold all of the spells you can currently cast, yet not so big it can't be carried by the character. Why worry about the page count and the weight? Even if you use the optional encumbrance rules, it would just be entered under 'miscellaneous encumbrance' (80cn weight, page X2) anyway.
So, forget about the nitnoy specifications of your spell books, just gather them up and get to adventuring already - the dungeon awaits!