Transaction Processing: Concepts and Techniques by Gray & Reuter is the definitive reference on transaction processing. The text book covers problems with OLTP systems and discusses fault tolerance, recovery, monitoring, concurrence, scheduling, and file systems. Includes a section on Guardian 90 in the Transaction Processing section.
A great reference to have sitting on the bookshelf, my only regret is that I did not have an opportunity to have my copy signed by Jim..