1. Operating System Introduction
-Compiled for CSIT
Ref: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc.

2. Content
1.1 Introduction Definition and Function, Two views of Operating System, Evolution/History and Types 1.2 System Calls

3. 1.1: Introduction

4. What Is An Operating System?
Lots of hardware !!
One or more processors
Main memory
Disks
Printers
Various input/output devices
Managing all these components requires a layer of software – the operating system

5. Where is the software?
Where the operating system fits in.

6. Functions of operating system
Process management
Process creation, deletion, suspension and resumption
Process synchronization and inter process communication
Process interactions – deadlock detection, avoidance and correction
Mutitasking
Memory management
Allocate and deallocate memory to process
Manage multiple processes within the memory
Manage the sharing of memory between processes
Determine which processed to load when memory is available

7. Functions of operating system
Storage Management
Directory / File creation and deletion
File system management
File/directory manipulation
Backup and achieve
Free-space management
Disk scheduling
I/O management
Device driver installation
Device interface and management

8. Functions of operating system
Protection and security
File attribute for accidental modification
Provides policy for user
Authentication
Data encryption
Firewall
Networking
Provides different sets of protocols that are used for secure networking
TCP/IP, FTP, POP, SMTP
Interface
CUI
GUI
Interactive

9. Two Views of OS
OS as Extended Machine
OS as Resource Manager

10. The Operating System as an Extended Machine

11. The Operating System as a Resource Manager
Allow multiple programs to run at the same time
Manage and protect memory, I/O devices, and other resources
Multiplexes (shares) resources in two different ways:
In time
In space

12. History of Operating Systems
Generations:
(1945–55) Vacuum Tubes
(1955–65) Transistors and Batch Systems
(1965–1980) ICs and Multiprogramming
(1980–Present) Personal Computers, Tablets, Phones

13. Transistors and Batch Systems (1)
Figure 1-3. An early batch system. (a) Programmers bring cards to (b)1401 reads batch of jobs onto tape.

14. Transistors and Batch Systems (2)
Figure 1-3. (c) Operator carries input tape to (d) 7094 does computing. (e) Operator carries output tape to (f) 1401 prints output.

15. ICs and Multiprogramming
MULTICS
Timesharing CTSS (MIT)
Multics
UNix
Figure 1-5. A multiprogramming system with three jobs in memory.

16. More third generation . Time Sharing (CTSS) Multics Unix Linux MULTICS
Timesharing CTSS (MIT)
Multics
UNix .

17. Fourth generation . PCs Network Operating Systems
Distributed Operating Systems
MULTICS
Timesharing CTSS (MIT)
Multics
UNix .

18. The Operating System Types
Mainframe operating systems
Big-thousands of disks….
Lots of jobs with lots of I/O
Services-batch (payroll) transactions (airline reservations, timesharing (query database)
Elderly-Unix, Linux replacing them

19. The Operating System Types:

20. The Operating System Types:
Batch operating systems
The users of a batch operating system do not interact with the computer directly.
Each user prepares his job on an off-line device like punch cards and submits it to the computer operator.
To speed up processing, jobs with similar needs are batched together and run as a group.
Disadvantage:
Lack of interaction between the user and the job.
CPU is often idle, because the speed of the mechanical I/O devices is slower than the CPU.
Difficult to provide the desired priority.

21. The Operating System Types:
Server operating systems
Workstations
File, print, web servers
BSD, Linux, Windows
Multiprocessor operating systems
Use multiple cores

22. The Operating System Types:
PC operating systems-Linux, Mac, Windows
Smart phone operating systems- Android, iPhone, Blackberry
No hard disk
Palm, Symbian popular OS’s
Multiprogramming OS
Run multiple program on single core
Advantage: Reduce CPU idle time and utilize it
Disadvantage: Question of security and integrity of user programs and data.

23. The Operating System Types:
Real-Time OS-
Data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment.
The time taken by the system to respond to an input and display of required updated information is termed as response time.
Types:
Hard real-time:
Guarantee that critical tasks complete on time.
Secondary storage is limited or missing with data stored in ROM.
Virtual memory is almost never found.

24. The Operating System Types:
Soft real-time:
Soft real time systems are less restrictive.
Have limited utility than hard real-time systems.
Example: Multimedia, virtual reality, Advanced Scientific Projects like undersea exploration and planetary rovers etc.

25. The Operating System Types:
Embedded Operating System
An operating system for embedded computer systems.
Typically designed to be resource-efficient and reliable. Resource efficiency comes at the cost of losing some functionality or granularity that larger computer operating systems provide, including functions which may not be used by the specialized applications they run.
The hardware running an embedded operating system can be very limited in resources such as RAM and ROM
In order to take better advantage of the processing power of the CPU, software developers may write critical code directly in assembly.
Often times, embedded operating systems are written entirely in more portable languages, like C.
Unlike a desktop operating system, the embedded operating system does not load and execute applications. This means that the system is only able to run a single application.

26. The Operating System Types:
Smart Card Operating System
OS designed for smart card
Every smart card has an operating system.
The OS is the hardware-specific firmware that provides basic functionality as secure access to on-card storage, authentication and encryption.
Some cards allow writing programs that are loaded onto the smart card – just like programs on a computer.
Example: Javacard OS, MultOS(Multi-application OS)

27. Operating Systems Structure
Monolithic systems
A main program that invokes the requested service procedure.
A set of service procedures that carry out the system calls.
A set of utility procedures that help the service procedures.

28. Monolithic Systems

29. Easy for error detection
Layered Systems-THE operating system
Components are organized and module are layered them from one top to next
Module are not free to communicate directly without maintaining hierarchy
Easy for error detection

30. Layered Systems-THE operating system
Dijkstra’s the author

31. Layered Systems

32. Microkernels

33. Microkernels Small number of processes are allowed in the kernel
Minimizes effects of bugs
Don’t want bug in driver to crash system
Put mechanism in kernel and policy outside the kernel
Mechanism- schedule processes by priority scheduling algorithm
Policy-assign process priorities in user space

34. Microkernels
Structure of the MINIX 3 system.

35. Microkernels

36. Client-Server Model
Divide operating kernel into several process
I/O server, memory server, thread interface server, print server etc
Servers run in user mode provide service when client demands

37. Client-Server Model
The client-server model over a network.

38. Virtual Machines (1)
The structure of VM/370 with CMS.

39. Virtual Machines (2)
(a) A type 1 hypervisor. (b) A type 2 hypervisor.

41. 1.2: System Call

42. What is System Call
A system call is the programmatic way in which a computer program requests a service from the kernel of the operating system it is executed on.
A system call is a way for programs to interact with the operating system.
A computer program makes a system call when it makes a request to the operating system’s kernel.
System call provides the services of the operating system to the user programs via Application Program Interface(API).
It provides an interface between a process and operating system to allow user-level processes to request services of the operating system.
System calls are the only entry points into the kernel system. All programs needing resources must use system calls.

43. Kernel mode and User Mode
Every modern OS supports Kernel Mode and User Mode

44. Kernel Mode
When CPU is in kernel mode, the code being executed can access any memory address and any hardware resource. 
Hence kernel mode is a very privileged and powerful mode.
If a program crashes in kernel mode, the entire system will be halted.

45. User Mode
When CPU is in user mode, the programs don't have direct access to memory and hardware resources. 
In user mode, if any program crashes, only that particular program is halted.
That means the system will be in a safe state even if a program in user mode crashes.
Hence, most programs in an OS run in user mode.

46. Service Provided By System Calls
Process creation and management
Main memory management
File Access, Directory and File system management
Device handling(I/O)
Protection
Networking, etc.

47. Types:
Process control: end, abort, create, terminate, allocate and free memory.
File management: create, open, close, delete, read file etc.
Device management
Information maintenance
Communication

48. Examples of windows and unix system call