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The chapter on the kernel model describes the abstract model implemented by the kernel.Lastly, the implementation chapter is a quick overview of the implementation techniques used in Amber.As an example of the former, all networking in Ethos is encrypted, authenticated, and authorized.
In contrast, over this time Programming Langugages (PLs) have adopted higher level, more abstract, semantics.
As a consequence of this semantic gap, PLs have been incorporating more OS semantics.
The security goal should go without saying, except that all too many systems that attempt to provide Isolation and Access Control provide them so long as a user does not take advantage of bugs or holes in the system that subvert the protection mechanisms.
Sometimes these holes are not just small implementation errors, but basic flaws in the system architecture.
Additional goals for the system were that it support various modes of usage: The scale and capabilities of the S-1 processor suggested that these various modes of usage occur concurrently as far as possible.
It was clear from the outset that a system as large as the S-1 would often be shared by more than one community of users.The Amber Design team, the original six: Ted Anderson, Jeff Broughton, Hon Wah Chin, Lee Parks and Daniel Weinreb. The later additions, Earl Killian and Jay Pattin, who joined in spite of the obvious problems. Very few large multifunction operating systems have been created from scratch in recent years.The expense, the belief that such systems are too complex, the emergence of "portable" operating systems, and the trend toward single user computers are all factors against building such systems.But PLs are not OSs; and a PL-as-OS approach forfeits advantages which result from new OSs.An OS's system calls (and other interfaces) define its semantics.The structure chapter describes the kernel concept and explains why it was adopted for Amber.The features chapter describes in detail what features we felt were important to have in the system and why.There is also another set of goals decided on by the design team itself: Note that achieving sharing while at the same time providing access control makes both more difficult.Sharing could easily be provided by allowing all users to read or write all data in the system and access control could be provided by forbidding any user from accessing data other than his own.For decades, Operating Systems (OSs) have stressed backward compatibility and extraordinary flexibility.Thus the semantics of today's widely-used OSs dates back to the 1970s.