16-05-2013, 01:50 PM
INTRODUCTION AND OVERVIEW OF OPERATING SYSTEMS
INTRODUCTION AND OVERVIEW.pptx (Size: 375.5 KB / Downloads: 14)
Abstract Views of an Operating System
What is an OS?
Abstract views
To a college student: SW that permits access to the Internet
To a programmer: SW that makes it possible to develop programs on a computer system
To a user of an application package: SW that makes it possible to use the package
To a technician in a computerized chemical plant: invisible component of a computer system that controls the plant
An abstract view focuses only on essential characteristics
Efficient Use
OS ensures efficient use of memory, CPU, and I/O devices
Poor efficiency can result if a program does not use a resource allocated to it
OS itself consumes CPU and memory resources, which constitutes overhead
It reduces resources for user programs
OS can monitor use of resources to ensure efficiency
It would increase the overhead
OS uses policies that ensure efficiency
Resource Management
Popular resource allocation strategies:
Resource partitioning
OS decides a priori what resources to allocate to each user program; divides system resources into partitions
A resource partition is a collection of resources
Resource table contains entries for partitions
Simple to implement, but lacks flexibility
Pool-based
OS allocates resources from a pool of resources
Consults table and allocates the resource if it is free
Less overhead of allocating and deallocating resources
Achieves more efficient use of resources