Chapter 13

Chapter 13

Operating Systems: An Overview

The Architecture of Computer Hardware and Systems Software:

An Information Technology Approach 3rd Edition, Irv Englander

John Wiley and Sons 2003

Wilson Wong, Bentley College

Linda Senne, Bentley College

Bare Bones Computer System

 Does not load instructions into main memory

 No user interface except for I/O routines provided with executing program

 Is idle when waiting for user input

 No facility to store, retrieve, or manipulate files

 No ability to control peripheral devices

Integrated Computer Environment

Operating System – Basic Services

 Programs that accept commands and requests from a user and a user’s

program

 Manages, loads, and executes programs

 Manages hardware resources of the computer

 Act as an interface between the user

Operating System – Additional Services

 Provides interfaces for the user and the user’s programs

 File support services

 I/O support services

 Means of starting the computer

 Bootstrapping or booting the computer

 Initial Program Load (IPL)

 Handles all interrupt processing

 Network services

 Provides tools and services for concurrent processing

Additional Services Required by Concurrent Processing

 Allocates resources such as memory, CPU time, and I/O devices to programs

 Protects users and programs from each other and provides for inter-program

communication

 Provides feedback to the system

administrators to permit performance

OS Parts

 Memory Resident

 Always loaded in memory

 Commonly called the kernel

 Contains essential services required by other parts of the operating system and applications.

 Typically responsible for managing memory management, processes and tasks, and secondary storage

 Memory Non-resident

 Applications

 Infrequently used programs, software tools, and commands

 Bootstrap program

 Diskless workstations or thin clients

 Programs, including the OS, are located on another computer on the

network

Simplified Diagram of Operating

System Services

OS Degree of Activity

 Interactive

 Also known as conversational systems

 Batch processing

 User submits programs or jobs for processing

 Little to no user interaction

 Event driven

 Interrupts or service requests

Hardware and the OS

 A hardware platform may support a variety of operating systems

 An operating system may work on a variety of platforms

 A standard operating system that works on different hardware

 Provides program and file portability

 Enables user efficiency through recognizable interface

 Is implemented through a systems programming language

like C or C++ as opposed to assembly language

Single Job Processing

 Only one program is loaded into memory and executed

 Example: MS-DOS

 Memory resident components

 Command interface shell

 I/O routines, including BIOS

 File management system

 User program in control

OS Regains Control

 When program is finished control is transferred back to the command interpreter

 If the user’s program requests I/O

 The user wishes to stop the program execution via a keyboard interrupt

 System malfunctions

Single Job Processing

Disadvantages

 Lack of security

 Programs can overwrite the resident OS

 Programs can write directly to I/O devices

 System provides minimum memory management and no scheduling

 CPU is often idle awaiting the completion of

I/O operations

Concurrent Operations

 Multitasking (multiprogramming) vs.

multiprocessing which implies multiple CPUs

 Concurrent processing vs. simultaneous

processing

Achieving Multitasking

 While one program is waiting for I/O to take place, another program is using the CPU to execute instructions.

 Time-slicing. The CPU may be

switched rapidly back and forth between different programs

 Dispatching is the process of selecting

which program to run at any given

Sharing the CPU during I/O Breaks

 I/O represents a large percentage of a

typical program’s execution

Time-sharing the CPU

Time slicing

Services and Facilities

 Command processor

 File management system

 I/O control system

 Process control management and interprocess communication

 Memory management

 Scheduling system

 Secondary storage management

 System protection management

 Network management, communication support, and

communication interfaces

User Interface and

Command Execution Services

 Types of user interfaces

 CLI - Command Line Interface

 GUI - Graphical User Interface

 Menu environment

 Shell

 User interface and command processor that interacts with the kernel

 UNIX: C, Bourne and Korn shells

 Command Languages

 IBM Mainframes – JCL

 MS Windows – BAT files, Windows Scripting Host

File Management

 File - logical unit of storage

 Basic file management system provides

 Directory structures for each I/O device

 Tools to copy and move files

 Information about each file in the system and the tools to access that information

 Security mechanisms to protects files and control access

 Additional file management features

 Backup, emergency retrieval and recovery

 File compression

 Transparent network file access

 auditing

I/O Services and

Process Control Management

 I/O services

 Startup configuration

 Device drives that implement interrupts and provide other techniques for handling I/O

 Plug and play: hot swapping, hot plugging

 Process control management

 A process is an executing program

 A thread is an individually executable part of a process

 Interprocess messaging services

Memory Management

 Keeps track of memory

 Identifies programs loaded into memory

 Amount of space each program uses

 Available remaining space

 Prevents programs from reading and writing memory outside of their allocated space

 Maintains queues of waiting programs

 Allocates memory to programs that are next to be loaded

 Deallocates a program’s memory space upon

Scheduling

 High-level scheduling

 Placed in queue based on level of priority and eventually executed

 Dispatching

 Actual selection of processes that will be executed at any given time

 Preemptive – uses clock interrupts

 Non-preemptive – program voluntarily gives up control

 Context switching

 Transfer control to the process that is being dispatched

 Nonpreemptive: program voluntarily gives up control

 Preemptive: uses clock interrupt for multitasking

 Processing requirements

Secondary Storage and Security

 Secondary storage management

 Optimizes completion of I/O tasks for efficient disk usage

 Combination of hardware and software

 Security and protection services

 Protect OS from users

 Protect users from other users

 Prevent unauthorized entry to system

 Prevent unauthorized system use by authorized

Network and Communication Services

 TCP-IP protocol suite

 Locate and connect to other computers

 Access files, I/O devices, and programs from remote systems

 Support distributed processing

 Network Applications

 Email, remote login, Web services, streaming multimedia, voice over IP telephony, VPN

 Interface between communication software

System Administration Support

 System configuration and setting group

configuration policies

 Adding and deleting users

 Modifying user privileges

 System security

 Files systems management

 Network administration

 Backups

 Software installations and upgrades

 OS installations

(system generation), patches, and upgrades

 System tuning and

optimization

Monolithic Kernel

 Drawback: stability and integrity

 Examples:

 UNIX

 Windows NT

Hierarchical

 Requests pass through

intermediate layers

 Examples

 Multics

 Data General

Microkernel

 Minimum essential functionality

 Client-server system on same system

 Clients request services from microkernel which

passes message onto appropriate server

Mach OS Kernel

 Microkernel implementation

 Includes

 Message passing

 Interrupt processing

 Virtual memory management

 Scheduling

 Basic set of I/O drivers

 Macintosh OS X, IBM AIX on RS/6000

Types of Operating Systems

 Single user, single tasking

 Single user, multitasking

 Multi-user, multitasking

 Distributed systems

 Processing power distributed among computers in a cluster or network

 Network servers

 Real-time systems

Bootstrapping

 Execution begins with bootstrap loader (mini-loader, IPL) stored in ROM

 Looks for OS program in a fixed location

 Loads OS into RAM

 Transfers control to starting location of OS

 Loader program in OS used to load and

execute user programs

Bootstrapping

 Cold vs.

warm boot

(does not

retest the

system)

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