Chapter 3:

(1)

Chapter 3:

Operating Systems

Computer Science: An Overview Twelfth Edition

by

J. Glenn Brookshear Dennis Brylow

(2)

Chapter 3: Operating Systems

• 3.1 The History of Operating Systems

• 3.2 Operating System Architecture

• 3.3 Coordinating the Machine’s Activities

• 3.4 Handling Competition Among Processes

• 3.5 Security

(3)

Functions of Operating Systems

• Oversee operation of computer

• Store and retrieve files

• Schedule programs for execution

• Coordinate the execution of programs

(4)

Evolution of Shared Computing

• Batch processing

• Interactive processing

– Requires real-time processing

• Time-sharing/Multitasking

– Implemented by Multiprogramming

• Multiprocessor machines

(5)

Figure 3.1 Batch processing

(6)

Figure 3.2 Interactive processing

(7)

Types of Software

• Application software

– Performs specific tasks for users

• System software

– Provides infrastructure for application software – Consists of operating system and utility

software

(8)

Figure 3.3 Software classification

(9)

Operating System Components

• User Interface: Communicates with users – Text based (Shell)

– Graphical user interface (GUI)

• Kernel: Performs basic required functions – File manager

– Device drivers

– Memory manager

– Scheduler and dispatcher

(10)

Figure 3.4 The user interface act as an intermediary between users and the

operating system kernel

(11)

File Manager

• Directory (or Folder): A user-created bundle of files and other directories

(subdirectories)

• Directory Path: A sequence of directories within directories

(12)

Memory Manager

• Allocates space in main memory

• May create the illusion that the machine has more memory than it actually does

(virtual memory) by playing a “shell game”

in which blocks of data (pages) are shifted back and forth between main memory and mass storage

(13)

Getting it Started (Bootstrapping)

• Boot loader: Program in ROM (example of firmware)

– Run by the CPU when power is turned on

– Transfers operating system from mass storage to main memory

– Executes jump to operating system

(14)

Figure 3.5 The booting process

(15)

Processes

• Process: The activity of executing a program

• Process State: Current status of the activity

– Program counter

– General purpose registers

– Related portion of main memory

(16)

Process Administration

• Scheduler: Adds new processes to the process table and removes completed processes from the process table

• Dispatcher: Controls the allocation of time slices to the processes in the process table

– The end of a time slice is signaled by an interrupt.

(17)

Figure 3.6 Time-sharing between

process A and process B

(18)

Handling Competition for Resources

• Semaphore: A “control flag”

• Critical Region: A group of instructions that should be executed by only one

process at a time

• Mutual exclusion: Requirement for proper implementation of a critical region

(19)

Deadlock

• Processes block each other from continuing

• Conditions required for deadlock

1. Competition for non-sharable resources 2. Resources requested on a partial basis 3. An allocated resource can not be forcibly

retrieved

(20)

Figure 3.7 A deadlock resulting from competition for nonshareable railroad intersections

(21)

Security

• Attacks from outside

– Problems

• Insecure passwords

• Sniffing software – Counter measures

• Auditing software

(22)

Security

(continued)

• Attacks from within

– Problem: Unruly processes

– Counter measures: Control process activities via privileged modes and privileged

instructions