These are some miscellaneous notes on Keykos. The main online info is at Agorics and the University of Pennsylvania.

Keykos is an object based capability system. It was developed at Tymshare beginning about 1975. An engineering goal of Keykos was to subject a great deal of OS function to some protection discipline so as to allow safe rapid development in that area. Capability discipline was the only protection mechanism we knew that could do this.

Keykos is more like Mach than any other well know system. It is substantially more capability oriented even than Mach however. Like Mach it is built to run on bare hardware. Unlike Mach, Keykos exposes more of the hardware architecture so as to deliver function available from the hardware, that even Mach denies. EROS is a system that follows Keykos in many ways, and with interesting divergent tradeoffs. See the specs and the source. CapROS and Coyotos succeed Eros.

There are two engineering philosophies behind computers and computer languages:

Of course no one takes either of these two extreme positions, but the spectrum between the two positions is well populated.

KeyKos is very much from the first school here. Although it not a language in the classic sense it does determine how programs for the machine must be written. While a computer language prescribes all details of the syntax of a program, Keykos prescribes how the program communicates with programs and entities outside its address space.

The Keykos Architecture is a dense but rather complete description of the system. It seems to require several readings to absorb. Here is an introduction and link to the closest thing to a defining document.

Here are several attempts at Keykos introductions for computer scientists:

While Keykos was originally built for the IBM 370, the 390 Principles of Operation describe a later architecture that is compatible with the 370.

Some of my notes that bear on Keykos: