Operating Systems - Advanced Operating System - Lecture Slides, Slides of Computer Science

Download Operating Systems - Advanced Operating System - Lecture Slides and more Slides Computer Science in PDF only on Docsity!

Introduction to

Operating Systems

COMP755 Advanced OS

What does an Operating System do?

• An Operating System provides a logical environment for using the computer.
• If you are using a system with Linux (or Windows or Unix or Solaris or Android or whatever) , it doesn’t matter what hardware you are using, it still runs the same.
• Users work with logical concepts instead of physical hardware.

Purpose of an OS

• A program that controls the execution of application programs
• An interface between the user or applications and the hardware
• Masks the details of the hardware
• Allocates resources to programs

Functions of an OS

• Compatibility The OS provides a virtual machine allowing programs to run on a variety of machines.
• Convenience Provides an easy to use interface.
• Efficiency Allows resources to be used efficiently.
• Security

Restrict access to resources

OS Interface

• The user interface can be a simple command line or a highly functional GUI
• There is a programmatic interface to the OS
• The API provides many functions to perform just about everything a program does except computation
• Programming language libraries call the OS API to perform much of their functionality

Just a Program

• The operating system is a computer program.
• Most operating systems are large (sometimes very, very large) programs.
• Operating systems can execute privileged instructions to control the hardware.
• Operating system relinquishes control of the processor to execute other programs

10

“I think there is a world market for

about five computers.”

Thomas J. Watson (1945)

president of IBM

11

Hardware Leads the OS

• Because of the better performance of modern computers, the OS can provide more services.
• Older computers didn’t have the speed or storage to run the OS of today.

13

No Operating Systems

• Each program directly interfaced with the hardware.
• One person used the computer at a time.
• “Job Scheduling” was done with a clipboard
• Libraries of commonly used procedures were the first start of operating systems.

14

Monitor Programs

• The monitor was a program that loaded application programs into RAM.
• The monitor, or a small portion of it, remained in RAM while the application program ran.
• The monitor contained device drivers to simplify access to peripherals.
• When the program terminated, it would jump back to the monitor (or not).

16

Simple Batch Systems

• The user submits a job (written on punched cards) to the computer.
• The operating system would copy the input data to a disk.
• When a job completed, the OS would select one of the jobs from the disk and run it.
• Printed output from the job was written to the disk. When the program terminated, the output file was copied to the printer.

17

Job Control Language (JCL)

• JCL was used to specify commands to the operating system
• The first characters of the input card identified it as JCL or data
• The JCL specified what program was to be run or what data file was to be used

19

Multiprogrammed Batch Systems

• Several programs had to be kept in RAM at the same time, each protected from the other.
• The OS had to be able to switch from one user environment to another.
• Relied on hardware that supports I/O interrupts and DMA

Software Engineering

• OS/360 was one of the first large (over 1000 programmers) software projects
• Fred Brooks claims in The Mythical Man Month that he made a multi-million dollar mistake of not developing a coherent architecture before starting development

Wikipedia, History of SEDocsity.com