os module 1

• Operating system


  A program (software) that acts as an intermediary (interface) between a user of a computer and the computer hardware
• Operating system provides

  An environment in which a user may execute programs
• Computer system components

  • Hardware - provides basic computing resources
  • Operating System - controls and coordinates the use of the hardware
  • Application programs - define the ways in which the system resources are used to solve the computing problems of the users
  • Users (people, machines, and other computers)
• Operating system goals


  • To provide a convenient environment
  • To use the computer hardware in an efficient manner (ensuring good performance)
• Resource allocator


  Manages and allocates resources, each program gets time and space with the resource
• Control program


  Controls the execution of user programs and operation of I/O devices to prevent errors and improper use of computer
• Kernel


  The one program running at all times, all else being application programs
• Growth of mainframe systems

  • Batch Systems
  • Multiprogrammed Systems
  • Time-sharing Systems
• Running a job in early mainframes

  1. Write a program in paper

  2. Punch program on cards

  3. Bring the card deck to the operator

  4. Card deck is read into the CPU

  5. Computer executes the job

  6. Output is produced

  7. Operator gets the output and gives it to the programmer

  8. Operator takes in another job
• Batch systems


  First rudimentary operating systems, reduce set-up time by batching similar jobs, machine runs only one application, automatic job sequencing, resident monitor
• Multiprogrammed batch systems


  Several jobs are kept in the main memory at the same time, the CPU is multiplexed (partitioned) among them
• Multiprogramming


  Some commands are executed from one program, then that program is suspended, and then some commands are executed from the next program, and so on, allows the CPU to process multiple programs
• OS features needed for multiprogramming

  • Job Scheduling
  • Memory Management
  • CPU Scheduling
  • Allocation of devices
• Time-sharing systems


  Allow many users to share one machine simultaneously, the CPU is multiplexed among several jobs that are kept in memory and on disk, on-line communication between the user and the system
• 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 of protection features, many run several different types of operating systems
• Parallel systems


  Multiprocessor systems with more than one CPU in close communication, tightly coupled system - processors share memory and a clock, symmetric multiprocessing (SMP) - each processor runs an identical copy of the operating system, asymmetric multiprocessing - each processor is assigned a specific task
• 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 communication lines, provides resource sharing, computation speed up, reliability, communications, requires networking infrastructure, may be either client-server or peer-to-peer systems
• Clustered systems


  Clustering allows two or more systems to share storage, provides high availability, asymmetric clustering - one server runs the application while another server is on standby mode, symmetric clustering - all N hosts are running that application and monitoring each other
• Real-time systems


  Often used as control devices in a dedicated application, well-defined fixed-time constraints, may either be hard or soft real-time, hard real-time - secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM), soft real-time - limited utility in industrial controls or robotics, useful in applications (multimedia, virtual reality) requiring advanced operating-system features
• Handheld systems


  Example: Personal Digital Assistants (PDAs), Cellular Telephones, issues: limited memory, Microsoft Windows CE Version 3.0, Pocket Internet Explorer, Pentium Class 206 MHz Intel StrongArm processor, 32MB RAM, 32MB to 128MB Compact Flash Disk, operates from a NiMH rechargeable battery pack for up to 40+ hours, integrated Ethernet connectivity
• Computing environments


  • Traditional Computing
  • Web-based Computing
  • Embedded Computing