4.1. Protected Objects and Methods of Protection
We begin by considering the history of protection in operating systems. This background helps us understand what kinds of things operating systems can protect and what methods are available for protecting them.
A Bit of History
Once upon a time, there were no operating systems: Users entered their programs directly into the machine in binary by means of switches. In many cases, program entry was done by physical manipulation of a toggle switch; in other cases, the entry was performed with a more complex electronic method, by means of an input device such as a keyboard. Because each user had exclusive use of the computing system, users were required to schedule blocks of time for running the machine. ...
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