Dear textbook authors...

I can sympathize with having some typos in the book — I've corrected dozens of them in mine.  I can even sympathize with having some typos in the on-line solutions manual (although that ought to be easier and quicker to correct — so why are the typos I reported to you a year ago still in it?).  I can sympathize with thinking up a new, interesting exercise to add to the textbook in later editions.  But when I add a new exercise to my textbook, I leave the old ones where they were.  I don't change them (except to correct typos).

I'm teaching this semester out of Hennessy & Patterson's Computer Organization and Design, which is well regarded in the field and has lots of good information — but which also has a reputation in the field for lots of typos.  So I'm using the Fourth Edition, Revised Printing.  One (or more) of the students in my class is using the Fourth Edition, without the words "Revised Printing" on the cover.  I didn't think that would be a serious problem, but it turns out that many of the questions I assigned are substantially different — although about the same topic — in his edition from mine.  And I can't always tell from his solutions what questions he was answering.