KeyKos and its ilk

The KeyKos Architecture” is a paper that appeared in the October 1985 Operating Systems Review. It is a high density introduction to the architecture of KeyKos.
Here is perhaps the most complete collection of papers about Keykos.
Here are yet more.
The Keykos programming manual is here. I am looking for an URL for Hydra, C.mmp (See “Hydra” in here.)
William Allan Wulf, Hydra C.mmp: An Experimental Computer System, McGraw Hill,
June 1981 ISBN: 0070721203
This book is out of print and I would appreciate any leads to where copies can be had.

The following book describes several capability based systems and their software.

Henry M. Levy, Capability Based Computer Systems, Digital Press, 1984.

Juicy History of Windows