The Operating Systems Handbook

This is an excellent overview of various obsolete mainframe operating systems (not to mention Unix, which is not obsolete.) You know the systems I mean: the ones you access using those ugly old green and black screens in a dusty corner of your IT department's offices, the ones with the humongous databases hidden behind arcane text-based software. The potentially dry material is greatly moistened by DuCharme's witty yet understated writing style.There are still a lot of those dinosaur mainframes still roaming the earth, Y2K notwithstanding, so this field guide is still useful, a full half-decade after it was published.

If you want to have a good overview of all the major mini/mainframe OSes, this is the book. The absence of NT and the inclusion of VM is questionable but this could be addressed by a 2nd edition. If you are looking for an in-depth discussion of the internals of each system this is not your book. But if you need to navigate multiple OSes in a multiplatform environment this is your best bet.