CIS340 Operating Systems

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Demo Lecture

Introduction to Operating Systems

About This Lecture

This lecture contains material which has been modified from slides copyright Silberschatz, Galvin and Gagne, 2001.  It covers the following topics:

• What is an Operating System?
• Mainframe Systems
• Desktop Systems
• Multiprocessor Systems
• Distributed Systems 
• Clustered Systems
• Real-Time Systems
• Handheld Systems
• Computing Environments

Before you begin

Exposure to a programming language is desirable background for this course.
 

Lecture Menu

About this Lecture

Learning Objectives

What is an Operating System?

Mainframe Systems

Desktop Systems

Multiprocessor Systems

Distributed Systems

Clustered Systems

Real -Time Systems

Handheld Systems

Computing Environments

Summary

Review Questions

Practice Test & Answers

Required Readings

After completing Lecture I, you will have a basic understanding of:

• operating systems
• the history of operating systems
• various different computing environments.

What is an Operating System?

• A program that acts as an intermediary between a user of a computer and the computer hardware.
• Operating system goals:
• Execute user programs and make solving user problems easier.
• Make the computer system convenient to use.
• Use the computer hardware in an efficient manner.

Computer System Components

1. Hardware – provides basic computing resources (CPU, memory, I/O devices).
2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users.
3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs).
4. Users (people, machines, other computers). 
 

Abstract View of System Components:

Operating System Definitions

• Resource allocator – manages and allocates resources.
• Control program – controls the execution of user programs and operations of I/O devices .
• Kernel – the one program running at all times (all else being application programs).

Mainframe Systems
 

• Reduce setup time by batching similar jobs
• Automatic job sequencing – automatically transfers control from one job to another.  First rudimentary operating system.
• Resident monitor
• initial control in monitor 
• control transfers to job 
• when job completes control transfers pack to monitor

Multiprogrammed Batch Systems:
Several jobs are kept in main memory at the same time, and the CPU is multiplexed among them.

OS Features Needed for Multiprogramming

• I/O routine supplied by the system.
• Memory management – the system must allocate the memory to several jobs.
• CPU scheduling – the system must choose among several jobs ready to run.
• Allocation of devices.

• The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory).
• A job swapped in and out of memory to the disk.
• On-line communication between the user and the system is provided; when the operating system finishes the execution of one command, it seeks the next “control statement” from the user’s keyboard.
• On-line system must be available for users to access data and code.

Desktop Systems
 

• Personal computers – computer system dedicated to a single user.
• I/O devices – keyboards, mice, display screens, small printers.
• User convenience and responsiveness.
• Can adopt technology developed for larger operating systems
• Often individuals have sole use of computer and do not need advanced CPU utilization or protection features.
• May run several different types of operating systems (Windows, MacOS, UNIX, Linux)

Parallel Systems:

• Multiprocessor systems with more than on CPU in close communication.
• Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory.
• Advantages of parallel systems: 
• Increased throughput
• Economical 
• Increased reliability
• graceful degradation
• fail-soft systems
• Symmetric multiprocessing (SMP)
• Each processor runs and identical copy of the operating system.
• Many processes can run at once without performance deterioration.
• Most modern operating systems support SMP
• Asymmetric multiprocessing
• Each processor is assigned a specific task; master processor schedules and allocates work to slave processors.
• More common in extremely large systems

Symmetric Multiprocessing Architecture:

Distributed Systems
 

• Distribute the computation among several physical processors.
• Loosely coupled system – each processor has its own local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines.
• Advantages of distributed systems.
• Resources Sharing 
• Computation speed up – load sharing 
• Reliability
• Communications
• Requires networking infrastructure.
• Local area networks (LAN) or Wide area networks (WAN)
• May be either client-server or peer-to-peer systems.

 

Clustered Systems
 

• Clustering allows two or more systems to share storage.
• Provides high reliability.
• Asymmetric clustering: one server runs the application while other servers standby.
• Symmetric clustering: all N hosts are running the application.

Real-Time Systems
 

• Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems.
• Well-defined fixed-time constraints (deadlines).
• Real-Time systems may be either hard or soft real-time.
• Hard real-time:
• Deadlines must always be met.
• Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM)
• Conflicts with time-sharing systems, not supported by general-purpose operating systems. 
• Soft real-time:
• An occasional missed deadline is allowable.
• Limited utility in industrial control of robotics
• Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.

• Personal Digital Assistants (PDAs)
• Cellular telephones
• Issues:
• Limited memory
• Slow processors
• Small display screens.

Computing Environments
 

• Traditional computing
• often networked PCs with servers for files and printing
• current technology is stretching the boundaries of traditional computing
• Web-Based Computing
• increased emphasis on networking
• Embedded Computing
• most prevalent form of computing
• found in automobiles, VCRs, robots, airplanes (fly by wire), microwave ovens and many other devices

Operating systems have been developed to ensure good system performance and to provide for user convenience.  They evolved from simple automatic job sequencing systems to sophisticated multiprogramming and time sharing systems.

Personal computer operating systems benefit from operating system technology for larger systems but do not require all features that larger systems do.

Systems for intensive computing may have many CPUs and include the categories of multiprocessor (parallel) systems, distributed systems and clustered systems.

Real-time systems are used in industrial process control, automated manufacturing, medical imaging and other applications.

Handheld systems are growing in popularity and have constraints of limited memory, slower processors and small displays.

Computing is done in a number of different environments, including traditional computing, web-based computing and embedded computing.
 

1.  What are three goals of an operating system?

2.  What are four computer system components?

3.  What do multiprogrammed batch systems do?

4.  What kind of multiple CPU system is tightly coupled and what kind loosely coupled?

5.  What are three computing environments?
 
 
 

1.  What are the three main purposes of an operating system?

2.  List the four steps that are necessary to run a program on a completely dedicated machine.

3.  In a multiprogramming and time-sharing environment, several users share the system simultaneously.  This situation can result in various security problems.  What are two such problems?

4.  What is the main advantage of multiprogramming?

5.  What are the main differences between operating systems for mainframe computers and personal computers?
 
 

Answers

1.  There are several possible purposes of an operating system:

• To provide an environment for a computer user to execute programs on computer hardware in a convenient and efficient manner.
• To allocate the separate resources of the computer as needed to solve the problem given. The allocation process should be as fair and efficient as possible.
• As a control program it serves two major functions: 1) supervision of the execution of user programs to prevent errors and improper use of the computer, and 2) management of the operation and control of I/O devices.

2.
a. Reserve machine time.
b. Manually load program into memory.
c. Load starting address and begin execution.
d. Monitor and control execution of program from console.
 

3.  Stealing or copying one’s programs or data; using system resources (CPU, memory,
disk space, peripherals) without proper accounting.
 

4.  Multiprogramming makes efficient use of the CPU by overlapping the demands for the CPU and its I/O devices from various users.  It attempts to increase CPU utilization by always having something for the CPU to execute.

5.  Personal computer operating systems are not concerned with fair use, or maximal use, of computer facilities. Instead, they try to optimize the usefulness of the computer for an individual user, usually at the expense of efficiency. Consider how many CPU cycles are used by graphical user interfaces (GUIs).  Mainframe operating systems need more complex scheduling and I/O algorithms to keep the various system components busy.
 
 
 

Read chapter 1 of Silberschatz et al.