Can a 20-year-old computer book still be relevant? Could be. The speed of machines and sophistication of software may have increased, but basic logic and computer architecture have remained the same since the beginning. This book lays out the essentials, plus a nice little section on the history of computation, which, among other things, lays to rest the canard that the Romans calculated with Roman numerals. (They used calculi [pebbles] on an abacus, in case you were wondering.)
The book is out of print, but there are lots of used copies kicking around out there, as you can see on the Amazon page.
HarperCollins, 200+ pages, paper.