The main memory is central to the operation of a modern computer system. main memory is a large array of bytes, ranging in size from hundreds of thousands to billions. Each byte has its own address. Main memory is repository of quickly accessible data shared by the CPU and I/O devices. The central processor reads instructions from main memory during the instruction fetch cycle and both reads and writes data from main memory during the data fetch cycle (on von Neuman architectures). The main memory is generally the only large storage device that the CPU is able to address and access directly. For example, for the CPU to process data from disk, those data must first be transferred to main memory by CPU generated I/O calls. In the same way, instructions must be in memory for the CPU to execute them.
For a program to be executed, it must be mapped to absolute addresses and loaded into memory. As the program executes, it accesses program instructions and data from memory by generating these absolute addresses. Eventually, the program terminates, its memory space is declared available, and the next program can be loaded and executed.
To improve both the utilization of the CPU and the speed of the computer's response to its users, general purpose computers must keep several programs in memory, creating a need for memory management. Many different memory-management schemes are used. These schemes reflect various approaches, and the effectiveness of any given algorithm depends on the situation. In selecting a memory-management scheme for a specific system, we must take into account many factors - especially the hardware design of the system. Each algorithm requires its own hardware support.
The operating system is responsible for the following activities in connection with memory management:
• Keeping track of which parts of memory are currently being used and who is using them • Deciding which processes (or parts of processes) and data to move into and out of memory • Allocating and deallocating memory as needed
About the Authors
Abraham Silberschatz is the Sidney J. Weinberg Professor of Computer Science at Yale University. Prior to joining Yale, he was the Vice President of the Information Sciences Research Center at Bell Laboratories. Prior to that, he held a chaired professorship in the Department of Computer Sciences at the University of Texas at Austin.
Professor Silberschatz is a Fellow of the Association of Computing Machinery (ACM), a Fellow of Institute of Electrical and Electronic Engineers (IEEE), a Fellow of the American Association for the Advancement of Science (AAAS), and a member of the Connecticut Academy of Science and Engineering.
Greg Gagne is chair of the Computer Science department at Westminster College in Salt Lake City where he has been teaching since 1990. In addition to teaching operating systems, he also teaches computer networks, parallel programming, and software engineering.
Operating System Concepts, now in its ninth edition, continues to provide a solid theoretical foundation for understanding operating systems. The ninth edition has been thoroughly updated to include contemporary examples of how operating systems function. The text includes content to bridge the gap between concepts and actual implementations. End-of-chapter problems, exercises, review questions, and programming exercises help to further reinforce important concepts. A new Virtual Machine provides interactive exercises to help engage students with the material.
Reader Adam Sinclair says, "
I'm writing this review from the perspective of a student. I am finishing an Operating Systems course at university and I have to say this book is fantastic at introducing new concepts. If there is ever a conversation about OS, I always refer to this book. The content is very well laid out and organized in a way that can be read from beginning to end. There is no need to jump from one chapter to another (unless you want to skip sections)."
Reader Chetan Sharma says, "
This book is bible for operating system knowledge. It covers very important concepts of Process Management and Memory Management. This book is good for all type of readers - Beginner, Intermediate and Advanced reader. Highly recommended for Students/Professionals/Readers who want to enhance their knowledge.