PEDIATRI

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An Operating Systems Vade Mecum

ion. Operating systems, like other software components, construct higher-level (virtual) resources out of lower-level (physical) ones. Details of the lower-level structures are hidden, and higher-level structures are introduced. From the point of view of a process, the physical machine is enhanced by the operating system into a virtual machine. Enhancement includes both simplicity (hiding details) and function (introducing new structures). Neither time (ability to execute) nor space (main store) appears to be shared with other processes. The virtual machine is thus simpler than the physical machine. The process interface provides extra instructions that improve on the basic hardware instruction set, particularly with respect to transput. The virtual machine is thus more functional than the physical machine. From the point of view of the user, the operating system provides services that are not present in the underlying machine. These services include loading and running programs, provi..

The Roscoe Operating System

Traditionally, a vade mecum (pronounced ‘‘VAHdee MAYkem’’) is a laboratory manual that guides the student step by step through complex procedures. Operating systems are complex mixtures of policy and mechanism, of algorithm and heuristic, and of theoretical goals and practical experience. This vade mecum tries to unify these diverse points of view and guide the novice step by step through the complexities of the subject. As a text, this book is intended for a first course in operating systems at the undergraduate level. The subject has so many individual parts that its practitioners and teachers often concentrate on subareas and ignore the larger concepts that govern the entire subject. I have tried to rectify that situation in this book by structuring the presentation about the dual ideas of resource management and beautification. To unify disparate threads of discussion, I have taken the liberty introducing names for recurrent themes and glorifying them with the title ‘‘principles.’ ’ I hope that this organization and nomenclature will help the reader to understand the subject better and to integrate new ideas into the same framework. Each technical term that is introduced in the text is printed in boldface the firs