Chapter 13 Operating Systems: An Overview

1. Chapter 13Operating Systems: An Overview The Architecture of Computer Hardware and Systems Software: An Information Technology Approach 3rd Edition, Irv Englander John Wiley and Sons 2003

2. 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 • Can run only one program at a time Chapter 13 Operating Systems: An Overview

3. Integrated Computer Environment Chapter 13 Operating Systems: An Overview

4. 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 and the system Chapter 13 Operating Systems: An Overview

5. 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 Chapter 13 Operating Systems: An Overview

6. 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 optimization of the computer system Chapter 13 Operating Systems: An Overview

7. 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 Chapter 13 Operating Systems: An Overview

8. Simplified Diagram of Operating System Services Chapter 13 Operating Systems: An Overview

9. 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 Chapter 13 Operating Systems: An Overview

10. 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 Chapter 13 Operating Systems: An Overview

11. 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 Chapter 13 Operating Systems: An Overview

12. 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 Chapter 13 Operating Systems: An Overview

13. 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 Chapter 13 Operating Systems: An Overview

14. Chapter 13 Operating Systems: An Overview

15. Concurrent Operations • Multitasking (multiprogramming) vs. multiprocessing which implies multiple CPUs • Concurrent processing vs. simultaneous processing Chapter 13 Operating Systems: An Overview

16. 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 instant Chapter 13 Operating Systems: An Overview

17. Sharing the CPU during I/O Breaks • I/O represents a large percentage of a typical program’s execution Chapter 13 Operating Systems: An Overview

18. Time-sharing the CPU Time slicing Chapter 13 Operating Systems: An Overview

19. 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 • System Administration Chapter 13 Operating Systems: An Overview

20. 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 • UNIX – shell scripts Chapter 13 Operating Systems: An Overview

21. 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 Chapter 13 Operating Systems: An Overview

22. I/O Services andProcess 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 • Example: a pipe in UNIX or DOS that is a temporary software connection between two programs or commands Chapter 13 Operating Systems: An Overview

23. 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 program completion Chapter 13 Operating Systems: An Overview

24. 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 • CPU vs. I/O bound Chapter 13 Operating Systems: An Overview

25. 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 users Chapter 13 Operating Systems: An Overview

26. 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 and OS I/O control system that provides network access Chapter 13 Operating Systems: An Overview

27. 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 System Administration Support Chapter 13 Operating Systems: An Overview

28. Monolithic Kernel • Drawback: stability and integrity • Examples: • UNIX • Windows NT Chapter 13 Operating Systems: An Overview

29. Hierarchical • Requests passthrough intermediatelayers • Examples • Multics • Data General Chapter 13 Operating Systems: An Overview

30. Microkernel • Minimum essential functionality • Client-server system on same system • Clients request services from microkernel which passes message onto appropriate server Chapter 13 Operating Systems: An Overview

31. 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 Chapter 13 Operating Systems: An Overview

32. 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 • Embedded systems Chapter 13 Operating Systems: An Overview

33. 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 Chapter 13 Operating Systems: An Overview

34. Bootstrapping • Cold vs.warm boot(does not retest the system) Chapter 13 Operating Systems: An Overview