1. Chapter 1 Basic Concepts of Operating Systems

2. Software
A program is a sequence of instructions that enables the computer to carry out some specific task.
Before a program executes, it has to be translated from its original text form (source program/code) into a machine language program (object program/code). Then, the program needs to be linked and loaded into memory.

3. Software Components
The software components are the collection of programs that execute in the computer.
These programs perform computations, control, manage, and carry out other important tasks.
Two general types of software components are:
System software
Application software

4. System Software
The system software is the set of programs that control the activities and functions of the various hardware components, programming tools and abstractions, and other utilities to monitor the state of the computer system.
The system software forms an environment for the programmers to develop and execute their programs (collectively known as application software).
Three types of users can be identified: system programmers, application programmers and end-users.

5. Application Software
Application software are the user programs and consist of those programs that solve specific problems for the users and execute under the control of the operating system.
Application programs are developed by individuals and organizations the ways in which the system resources are used to solve the computing problems of the users
Word processors, compilers, web browsers, database systems, video games
Users
People, machines, other computers

6. Computer System Structure
Computer system can be divided into four components:
Hardware – provides basic computing resources
CPU, memory, I/O devices
System software - Operating System, Assemblers, Loaders, Linkers, Compilers, Editors, …
Operating system
Controls and coordinates use of hardware among various applications and users
Application programs – All User-Oriented Programs, which define the ways in which the system resources are used to solve the computing problems of the users
Word processors, compilers, web browsers, database systems, video games
Users
People, machines, other computers

7. Computer System Structure
System software - Operating System, Assemblers, Loaders, Linkers, Compilers, Editors, …
Application software - All User-Oriented Programs.
SYSTEM and APPLICATION PROGRAMS
Users
SYSTEM PROGRAMS/OS
HARDWARE

8. Operating System Definition (Cont.)
No universally accepted definition
“Everything a vendor ships when you order an operating system” is a good approximation
But varies wildly
“The one program running at all times on the computer” is the kernel.
Everything else is either
a system program (ships with the operating system) , or
an application program.

9. External View of a Computer
Kernel

10. What is an Operating System?
A large and complex set of software component for the operation and control of the computer system. Availability of services and Management of the computer resources
OS is a resource allocator
Manages all resources
Decides between conflicting requests for efficient and fair resource use
OS is a control program
Controls execution of programs to prevent errors and improper use of the computer
It acts as an intermediary between a user and the computer system.

11. Design Goals
User goals – operating system should be convenient to use, easy to learn, reliable, safe, and fast.
System goals – operating system should be easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient.

12. What Operating Systems Do
Depends on the point of view
Users want convenience, ease of use and good performance
Don’t care about resource utilization
But shared computer such as mainframe or minicomputer must keep all users happy
Users of dedicate systems such as workstations have dedicated resources but frequently use shared resources from servers
Handheld computers are resource poor, optimized for usability and battery life
Some computers have little or no user interface, such as embedded computers in devices and automobiles

13. Operating Systems User Interfaces
User and application programmers can communicate with OS via interface
Three levels of interface:
Graphical User Interface: GUI (windows oriented)
Command line level interpreter (also known as the shell). At login time, the shell starts computing
System calls interface invoked from user programs

14. Basic Structure of an OS
The GUI and the Shell are at the same level in the structure of an OS

15. GUI The first and the highest level of is the GUI
Allow interaction via icons, menu, and other graphical objects
This level of OS interface is not considered as essential part of the Operating System, it is rather an add-on system software component.

16. The Shell
The second level of interface, the command line interpreter, or Shell program that handles user interaction with the system is called:
Shell
Command-line interpreter
Two types of Shells
Graphical
Character oriented

17. System Calls
The third level, the System –call interface, is used by the application programs to request services provided by the OS by invoking or calling system functions. This is also known as the Application Programming Interface (API)
Programs use the API to request the OS to perform some function

18. Common Functions of Interrupts
Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines
Interrupt architecture must save the address of the interrupted instruction
A trap or exception is a software-generated interrupt caused either by an error or a user request
An operating system is interrupt driven

19. Interrupt Handling
The operating system preserves the state of the CPU by storing registers and the program counter
Determines which type of interrupt has occurred:
polling
vectored interrupt system
Separate segments of code determine what action should be taken for each type of interrupt

20. Interrupt Timeline

21. Multi-Level Views
The overall structure of an operating system is divided into the various software components using a top-down (layered) approach.
The top layer provides the easiest interface to the human operators and users interacting with the system.
Any layer uses the services or functions provided by the next lower layer.

22. Operating Systems Abstract Views
External views (Sometimes refer to as the abstract views)
Abstraction provides by the OS interfaces gives users and application programs the appearance of a simpler machine.
Set of interface of the computer system
A layer of software on top of the hardware
Internal view
System call interface separates the kernel from the application layer
Resource manager - It controls and manages CPU, memory, I/O devices, etc.

23. Abstract Views of an OS

24. Transition from User to Kernel Mode
Timer to prevent infinite loop / process hogging resources
Timer is set to interrupt the computer after some time period
Keep a counter that is decremented by the physical clock.
Operating system set the counter (privileged instruction)
When counter zero generate an interrupt
Set up before scheduling process to regain control or terminate program that exceeds allotted time

25. Layered Structure of an OS
Users (top layer)
Application User Interface (AUI): shell, commands, application programs
Application program Interface (API): libraries, system calls
OS kernel

26. Internal View of an Operating System
The system call interface separates the kernel from the application layer and the kernel is located above the hardware
The kernel is the core and most critical part of the operating system and needs to be always resident in memory.
A detailed knowledge about the different components, including these lower-level components of the operating system, correspond to an internal view of the system.

27. Functional Components of an OS
The most important components of an operating system are:
Process manager
Memory manager
Resource manager
File manager
Device manager

28. Services Provided by the OS
Process Control, execution, scheduling, etc.
Communication between processes
File Manipulation
Device Manipulation
Information Maintenance
Memory Management

29. Jobs and Processes
A job is a unit of work submitted by a user to the operating system. A typical job consists of the parts listed below:
A sequence of commands to the operating system
A program either in a source language or in binary form
A set of input data used by the program when it executes
A process basically refers to an execution instance of a program.

30. Categories of Operating Systems
Batch systems, in which a set of jobs are submitted in sequence for processing. The system have long average turnaround period (interval from job arrival time to completion time) of jobs.
Interactive systems, which support computing for on-line users. The most common type of operating systems that support interactive computing is time-sharing, which are multi-user systems.
Real-time systems, which support application programs with very tight timing constraints.
Hybrid systems, which support batch and interactive computing.

31. A Time-Sharing System

32. Jobs
The term job refers to a unit of work submitted by a user to the operating system.
A typical job consist of the following:
A sequence of commands to the OS
A program either in a source language or in binary form
A set of input data used by the program when it executes

33. History of Operating Systems
First generation - No operating system, bare hardware, machine language.
Second generation
Batch systems, assemblers, linkers, loaders, compilers
Batch systems with Automatic Job Sequencing

34. History of Operating Systems(2)
Third generation -- O.S. for complete families of computers (OS/360)
Batch with Multiprogramming
Spooling
Timesharing (MULTICS, UNIX, …)
Fourth generation
Network and distributed operating systems

35. Modern Operating Systems
Windows (Microsoft Corporation) these include a family of systems: 98, Me, CE, 2000, XP, Vista, Windows 7, and others
Linux (Linus Torvalds, OSF GNU)
MacOS (Apple)
Solaris (Sun Microsystems)
OSF-1 (OSF, DEC)
IRIX (Silicon Graphics)
OS2 (IBM)
OS/390 (IBM)
VMS (Dec/Compaq/HP)

36. System Implementation
Traditionally written in assembly language, operating systems can now be written in higher-level languages.
Code written in a high-level language:
can be written faster.
is more compact.
is easier to understand and debug.
An operating system is far easier to port (move to some other hardware) if it is written in a high-level language.

37. Chapter 2 Processes and Threads

38. Processes & Threads
Processes and threads are two important types of dynamic entities in computer system.
A Process is a the execution of a Program; More specifically…
A process is a program in memory either
in execution
waiting for CPU, I/O, or other service.

39. Process Management
A process can contain one or more threads of execution in order to execute, partially is waiting for other services in the computer system.
An important function of the OS are:
It involves creating processes and controlling their execution
The OS manages several processes in memory at the same time
The processes share the system resources --- multiprogramming

40. Processes
Two important types of dynamic entities in a computer system are processes and threads.
The state changes are really controlled by the OS
When the process is needs a resources and is NOT available, the processes changes from one state of changes from the running state to the waiting for resource state
Then a process is waiting for service from the CPU, it is placed in the ready queue and is in the ready state.
Also, when a process is waiting in I/O service, it is placed in one of several I/O queue and it changes to wait state.

41. Process Creation On a typical operating system, a process is created
In response to a new job arriving
A new user who carries out a login
A currently executing process that creates a new process.
A process is created if there is sufficient memory available, and the process waits if other resources it needs are not available.

42. Process Behavior
A process requests CPU and I/O processing at various times and usually will have to wait for these services.
The OS maintains a waiting line or queue of processes for every one of these services.
At some point in time, the process will be in a queue waiting for CPU service. At some other point in time, the process will be in a different queue waiting for I/O service.
When the process completes all service requests, it terminates and exits the system.

43. Process States Created Ready (waiting in the ready queue for the CPU)
Running (executing)
Blocked (suspended and waiting for I/O or other event)
I/O processing
Waiting for passive resources
Interrupted by the OS
Terminated

44. Process State Diagram
Represents the various states of a process and the possible transitions in the behavior of a process.
Each state is indicated by a rounded rectangle and the arrows connecting the states are the transitions from one state to the next.
The small black circle denotes that the state it points to is the initial state.
In a similar manner, the state before the hollow small circle indicates that it is the last state in the behavior of a process.
Normally a process spends a short finite time in any of its states.

45. Process State-Transition Diagram
Process is created. In a time-sharing system, user logs New process is created.
Process is ready and waits for CPU services
Initial State
The state in which a program is waiting for I/O service is normally called the block state
After satisfying all service requests, the process terminates
It is possible wait state is defined when the process is swapped out to disk, if there is not sufficient memory.
Last State

46. Process Descriptor
Fro every new process in the system, a data structure called Process Descriptor, also known as a process control block (PCB)
The behavior of this process is that when the process terminates, its descriptor is normally destroyed.

47. Data in a Process Descriptor
Each process is represented by its own PCB
Process name
Process state
Program counter, CPU registers
I/O status
Memory information
Accounting information
Scheduler information (priority, queues, …)
List of resources

48. Process Descriptor

49. Threads Modern OS supports computational units called threads.
A process can have multiple threads or sequences of executions.
Threads often called:
A light-weight process
A single execution sequence
A component of a process
Shares with other threads code and resources allocated to the process
Most OSs support multi-threading: several threads in a single process

50. MultiThreading
In addition to multiple processes, newer operating systems support other computational units called threads.
A thread is called a lightweight process and is a dynamic component of a process.
The OS manages processes and threads in a multiprogramming environment.

51. Threads Executing in a Process
Threads behaves as a active elements of computation within a process.
All threads that belong to a program share the code and resources of the process

52. Thread Attributes
The thread identifier uniquely identifies the threads. Its attributes are as follow:
Execution state
Context, its own program counter within the process
Execution stack
Local memory block (for local variables)
Reference to parent process to access the shared resources allocated to the process

53. Thread Descriptor
A thread descriptor is a data structure used by the OS to store all the relevant data of a thread.
It contains the following fields:
thread identifier
execution state of the thread
the process owner of the thread
list of related threads
execution stack
thread priority
thread-specific resources
Some of the fields of a thread descriptor also appear as part of the corresponding process descriptor.

54. Thread States
Threads have their own execution state, context, execution stack, local memory (for local variables), in addition to the resources allocated to the process.
When a process is created, only one thread is created called the base thread of the process; then other threads of the process may be created by the process or by the base thread.
A process can have a single thread; in this case it is considered a simple process because it has only one thread of execution.

55. Types of Threads There are two general types of threads:
User-level threads (ULT) – the threads management is carried out at the application level without kernel innervation.
Kernel-level threads (KLT). the threads management is carried out by kernel.

56. User-level Threads
With the user-level threads, the thread management is carried out at the level of the application without kernel intervention.
The application carries out threads management using a thread library, such as the POSIX Pthreads Library.
Using this library, the application invokes the appropriate functions for the various thread management tasks such as: creating, suspending, and terminating threads.

57. Kernel-Level Threads
The thread management tasks are carried out by the kernel.
A process that needs these thread handling services has to use the API to the kernel thread facility.
One of the advantages of kernel-level threads is that the process will not be blocked if one of its threads becomes blocked. Another advantage is that the possibility of scheduling multiple threads on multiple CPUs.

58. Java Threads
A program can have multiple execution paths (Sequences of flow of control) call threads.
A typical Java application has multiple threads
A thread in Java is an object
Java provides several techniques to create and manipulate threads

59. POSIX Threads Are known as Pthreads, is not object oriented.
Developed for the C programming language
With C and C++, Pthreads is used as an external library that needs to be linked with the application.
The Psim3 (process simulation 3) package is used to implement the simulation model discussed in this book, that was developed with Pthreads.

60. Multi-programming
OS can support several processes in memory through a facility know as multiprogramming.
One of the requirements of multiprogramming is that the OS must allocate the CPU and other resources to the various processes in such a way that the CPU and other active resources are maintained busy the longest period possible.
If there is only one CPU in the computer system, then only one process can be in execution at any given time.
The other processes are ready, waiting for CPU service. Processes also request access to passive resources, such as memory.

61. Context Switch
When the CPU switches to another process, the OS must save the state of the current process and load the saved state of the new process
Context switch time is overhead time
Context switch time is dependent on hardware support

62. Degree of Multiprogramming
An operating system can support several processes in memory.
While one process receives service from the CPU, another process receives service from an I/O device and the other processes are waiting in some queues.
The number of processes that the system supports is called the degree of multiprogramming.

63. Features Needed for Multiprogramming
I/O routines supplied by the system
Memory management
CPU scheduling
Allocation of devices

64. Computing Environments
Allows operating systems to run applications within other OSes
Vast and growing industry
Emulation used when source CPU type different from target type (i.e. PowerPC to Intel x86)
Generally slowest method
When computer language not compiled to native code – Interpretation
Virtualization – OS natively compiled for CPU, running guest OSes also natively compiled
Consider VMware running WinXP guests, each running applications, all on native WinXP host OS
VMM (virtual machine Manager) provides virtualization services

65. Computing Environments
Use cases involve laptops and desktops running multiple OSes for exploration or compatibility
Apple laptop running Mac OS X host, Windows as a guest
Developing apps for multiple OSes without having multiple systems
QA testing applications without having multiple systems
Executing and managing compute environments within data centers
VMM can run natively, in which case they are also the host
There is no general purpose host then (VMware ESX and Citrix XenServer)

66. Computing Environments

67. Service Demands
A process will require several CPU and I/O requests (demands)
The total CPU request of a process is divided into shorter service periods: each one is called a CPU burst
The total I/O request is divided into shorter service periods called I/O bursts
In normal behavior of a process, it alternates between a CPU and I/O burst

68. Total I/O Service Demand
The total I/O service demand for a process is the sum of all its I/O bursts
Each I/O burst has a different duration, 
The total I/O service time requested by process Pi is:
i = 1 +  n

69. Batch OS with I/O

70. Interrupts and Context Switches
A context switch occurs when:
The running process completes its current CPU burst and needs an I/O operation, such as reading data from a file.
The running process is interrupted by a timer under OS control. The process returns to its ready state in the wait line for CPU service, the ready queue.
A high priority process arrives or is made to transition to the ready state, the OS interrupts the running process if it has a lower priority.

71. CPU and I/O Devices
Basic queues in the CPU and I/O devices that a process joins while waiting for service in the computer system.