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Operating Systems

Introduction

Chester Rebeiro

IIT Madras

Webpage : http://www.cse.iitm.ac.in/~chester/courses/15o_os/index.html

The Layers in Systems

VLSI

Computer Organization Transistors Operating Systems Applications

A Simple Program

What is the output of the following program?

How is the string displayed on the screen?

Displaying on the Screen

• (^) Can be complex and tedious
• (^) Hardware dependent Without an OS, all programs need to take care of every nitty gritty detail Processor Memory Processor Graphics Card Monitor “Hello World” “Hello World” + coordinates, color, depth, etc

OS as a Resource Manager

• Multiple apps but limited hardware

Operating Systems Apps A few processors

OS as Resource Manager

• OS must manage CPU, memory, network,

disk etc…

• Resource management

– allows multiple apps to share resources

– protects apps from each other

– Improves performance by efficient utilization

of resources

Operating Systems Types

• (^) Application Specific
  • (^) Embedded OS
    • (^) eg. Contiki OS, for extremely memory constraint environments
  • (^) Mobile OS
    • (^) Android, iOS, Ubuntu Touch, Windows Touch
  • (^) RTOS
    • (^) QNX, VxWorks, RTLinux
  • (^) Secure Environments
    • (^) SeLinux, SeL
  • (^) For Servers
    • (^) Redhat, Ubuntu, Windows Server
  • (^) Desktops
    • (^) Mac OS, Windows, Ubuntu

JOS and xv

• Designed for pedagogical reasons

• Unix like (version 6)

– Looks very similar to modern Linux operating

systems

• Theory classes : xv

– Well documented, easy to understand

• Lab : JOS

– Build your own operating system from the

skeleton

Textbooks / References

• (^) ''xv6: a simple, Unix-like teaching operating system" ,

Revision 8, by Russ Cox, Frans Kaashoek, Robert

Morris

• (^) ''Operating System Concepts'' , 8th edition, by

Adraham Silberschatz, Pert B. Galvin, and Greg Gagne,

Wiley-India edition

• (^) The xv6 source code booklet (revision 8) http://www.cse.iitm.ac.in/~chester/courses/15o_os/index.html

Logistics

• Theory Classes (CS24, Slot F)

– Wednesdays : 11:00 - 11:50 AM

– Thursdays : 9:00 - 9:50 AM

– Fridays : 8:00 - 8:50 AM

• Lab (System’s Lab, Slot P)

– Monday’s : 2:00 – 5:00 PMs

Operating Systems

(How did it all start?)

OS Evolution

• Evolution driven by Hardware improvements

+ User needs

– eg. low power requirements, Increased /

reduced security, lower latency

– Evolution by

• (^) New/better abstractions
• (^) New/better resource management
• (^) New/better low level implementations

Gen 1 : OS

• OS: Unheard of

• Human feeds program and prints output

George Ryckman, on IBM’s first computer The cost of wastage was $146,000 per month (in 1954 US Dollars)

Gen 2 : Mainframes

• Hardware

– transistors

• User Programs

– Assembly or Fortran entered using punch

cards

• OS : Batch systems

– Possibly greatest invention in OS

• (^) Computers may be able to schedule their own

workload by means of software