1. Lecture 2
Cs506

2. مواعيد المعمل
الاثنين : 2.30 الى 4 السبت : 5.30 الى 7

3. Computer-System Architecture

4. Computer-System Architecture
Single-Processor Systems
Multiprocessor Systems
Clustered Systems

5. Computer-System Architecture
1- Single general-purpose processor
On a single-processor system, there is one main CPU capable of executing a general-purpose instruction set, including instructions from user processes.
Most systems have special-purpose processors as well

6. Computer-System Architecture
2- Multiprocessors systems :
growing in use and importance
Also known as parallel systems, tightly-coupled systems
The system have two or more processors in close communication , sharing the computer bus memory and peripheral devices.
Advantages include
Increased throughput
Economy of scale
Increased reliability – graceful degradation or fault tolerance

7. Computer-System Architecture
Two types
Asymmetric Multiprocessing
Symmetric Multiprocessing
1- Asymmetric Multiprocessing
In which each processor is assigned a specific task.
A master processor controls the system
Master-slave relation ship
2- Symmetric Multiprocessing
All processors are peers
Many processes can run simultaneous … n processes can run if n
CPU

8. Symmetric Multiprocessing Architecture

9. Computer-System Architecture
- Multi-computing core
Multi processor per chip
Multi chips with single core
Which better? And why?
First
Because on-chip communication is faster than between- chips

10. A Dual-Core Design

12. Clustered Systems
3- Clustered Systems
Like multiprocessor systems, but multiple systems working together
A clustered system uses multiple CPUs to complete a task.
It is different from parallel system in that clustered system consists of two or more individual systems tied together.
Definition : The clustered computers share storage and are closely linked via LAN networking.

13. Clustered Systems
Provides a high-availability service which survives failures: A layer of cluster software runs on cluster nodes. Each node can monitor one or more nodes over the LAN.
The monitored machine can fail in some cases.
The monitoring machine can take ownership of its storage.
The monitoring machine can also restart applications that were running on the failed machine-
The failed machine can remain down but the users will see a brief of the service.

14. Clustered Systems The clustered system can be of the following forms:
Asymmetric clustering: In this form, one machine is in hot standby mode and other machine is running the application. The hot standby machine performs nothing. It only monitors the server. If failure It becomes the active server if the server fails.
Symmetric clustering In this mode, two or more machines run the applications. They also monitor each other at the same time. This mode is more efficient because it uses all available machines. It can be used only if multiple applications are available to be executed
high-performance computing (HPC)
Applications must be written to use parallelization

16. Operating System Structure

17. Operating System Structure
Multiprogramming
Multiprocessing
Multitasking

18. Operating System Structure
Multiprogramming:
Multiprogramming is a form of parallel processing in which several programs are run at the same time on a uniprocessor.
Since there is only one processor , there can be no true simultaneous execution of different programs. Instead, the operating system executes part of one program, then part of another, and so on.
To the user it appears that all programs are executing at the same time

19. Memory Layout for Multiprogrammed System

20. Operating System Structure
Multiprogramming needed for efficiency
Single user cannot keep CPU and I/O devices busy at all times
Multiprogramming organizes jobs (code and data) so CPU always has one to execute
A subset of total jobs in system is kept in memory
One job selected and run via job scheduling
When it has to wait (for I/O for example), OS switches to another job

21. Operating System Structure
Note :
Multiprogramming means: that several programs in different stages of execution are coordinated to run on a single I-stream engine (CPU).
Multiprocessing, which is the coordination of the simultaneous execution of several programs running on multiple I-stream engines (CPUs).

22. Operating System Structure
Timesharing (multitasking):
is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing

23. Operating System Structure
Timesharing:
Response time should be < 1 second
Each user has at least one program executing in memory process
If several jobs ready to run at the same time  CPU scheduling
If processes don’t fit in memory, swapping moves them in and out to run
Virtual memory allows execution of processes not completely in memory

24. Multiprograming
Running more then one program with in an application to perform a certain task.
Example : In MS WORD, Writing in document and sending
Multitasking
Running more then one application to perform a certain task.
Example: listening Song, playing game, work in ms word, excel and other applications simultaneously
Multiprocessing
Running more then one instruction through a processor.
Example When create a file then computer takes Time and date default.

25. Operating-System Operations

26. Computer-System Operation
Each device controller is in charge of a particular device type (disk drive, video displays etc).
I/O devices and the CPU can execute concurrently.
Each device controller has a local buffer.
CPU moves data from/to main memory to/from local buffers
I/O is from the device to local buffer of controller.
Device controller informs CPU that it has finished its operation by causing an interrupt.

27. Interrupt Means : cut off
Hardware interrupt, e.g. services requests of I/O devices
Software interrupt, e.g. signals, invalid memory access, division by zero, system calls, etc –(trap)
Procedures: generic handler or interrupt vector (MS-DOS,UNIX)

28. Operating-System Operations
Interrupts are an important part of a computer architecture.
Each computer design has its own interrupt mechanism, but several functions are common.

29. Operating-System Operations
Interrupt driven by hardware
Software error or request creates exception or trap
Division by zero, request for operating system service
Other process problems include infinite loop, processes modifying each other or the operating system

30. Common Functions of Interrupts
Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt
A trap is a software-generated interrupt caused either by an error or a user request
An operating system is interrupt driven

31. Operating-System Operations
Instruction Cycle with Interrupts 
CPU checks for interrupts after each instruction.
If no interrupts, then fetch next instruction of current program.
If an interrupt is pending, then suspend execution of the current program. The processor sends an acknowledgement signal to the device that issued the interrupt so that the device can remove its interrupt signal.
Interrupt architecture saves the address of the interrupted instruction (and values of other registers).

32. Operating-System Operations
Instruction Cycle with Interrupts 
Interrupt transfers control to the interrupt service routine (Interrupt Handler), generally through the interrupt vector, which contains the addresses of all the service routines.
Separate segments of code determine what action should be taken for each type of interrupt

33. Operating-System Operations
Interrupt Handler 
A program that determines nature of the interrupt and performs whatever actions are needed
Control is transferred to this program
Generally part of the operating system

34. Operating-System Operations: Interrupt Handling Procedure
Save interrupt information
OS determine the interrupt type (by polling)
Call the corresponding handlers
Return to the interrupted job by the restoring important information (e.g., saved return address program counter)

35. System Calls

36. System Calls System calls :
Interface between processes & OS
Definition: is how a program requests a service from an operating system’s kernel . They provide the interface between a process and operating system.
Is an interface between a user-space application and a service is provided in the kernel.

37. System Calls How to make system calls?
Assemble-language instructions or subroutine/functions calls in high-level language such as C or Perl?
Generation of in-line instructions or a call to a special run-time routine.
Example: read and copy of a file!
Library Calls vs System Calls

38. System Calls Programming interface to the services provided by the OS
Typically written in a high-level language (C or C++)

39. System Calls
Three most common APIs are Win32 API for Windows, POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM)
Why use APIs rather than system calls? (Note that the system-call names used throughout this text are generic)

40. API – System Call – OS Relationship

41. System Call Implementation
The system call interface invokes intended system call in OS kernel and returns status of the system call and any return values
The caller need know nothing about how the system call is implemented
Just needs to obey API and understand what OS will do as a result call
Most details of OS interface hidden from programmer by API
Managed by run-time support library (set of functions built into libraries included with compiler)

42. Example of Standard API
Consider the ReadFile() function in the
Win32 API—a function for reading from a file
A description of the parameters passed to ReadFile()
HANDLE file—the file to be read
LPVOID buffer—a buffer where the data will be read into and written from
DWORD bytesToRead—the number of bytes to be read into the buffer
LPDWORD bytesRead—the number of bytes read during the last read
LPOVERLAPPED ovl—indicates if overlapped I/O is being used

43. Standard C Library Example
C program invoking printf() library call, which calls write() system call

44. How System Call in Unix

45. System Call Parameter Passing
Three general methods used to pass parameters to the OS
Simplest: pass the parameters in registers
In some cases, may be more parameters than registers
Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register
This approach taken by Linux and Solaris
Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system
Block and stack methods do not limit the number or length of parameters being passed

46. Parameter Passing via Table

47. Types of System Calls Process control File management
Device management
Information maintenance
Communications
Protection

48. Examples of Windows and Unix System Calls

49. MS-DOS execution
(a) At system startup (b) running a program

50. FreeBSD Running Multiple Programs

51. System programs

52. System Programs
Provide a convenient environment for program development and execution
Some of them are simply user interfaces to system calls; others are considerably more complex
File management - Create, delete, copy, rename, print, dump, list, and generally manipulate files and directories

53. System Programs Status information
Some ask the system for info - date, time, amount of available memory, disk space, number of users
Others provide detailed performance, logging, and debugging information
Typically, these programs format and print the output to the terminal or other output devices
Some systems implement a registry - used to store and retrieve configuration information

54. System Programs (cont’d)
File modification
Text editors to create and modify files
Special commands to search contents of files or perform transformations of the text
Programming-language support - Compilers, assemblers, debuggers and interpreters sometimes provided

55. System Programs (cont’d)
Program loading and execution- Absolute loaders, reloadable loaders, linkage editors, and overlay-loaders, debugging systems for higher-level and machine language

56. System Programs (cont’d)
Communications - Provide the mechanism for creating virtual connections among processes, users, and computer systems
Allow users to send messages to one another’s screens, browse web pages, send electronic-mail messages, log in remotely, transfer files from one machine to another

57. User Operating System Interface

58. User Operating System Interface - CLI
1- Command Line Interface (CLI)
or command interpreter allows direct command entry
Sometimes implemented in kernel, sometimes by systems program
Sometimes multiple flavors implemented – shells

59. User Operating System Interface - CLI
Primarily fetches a command from user and executes it
Sometimes commands built-in, sometimes just names of programs
If the latter, adding new features doesn’t require shell modification

60. User Operating System Interface - GUI
2- Graphical User Interface (GUI )
User-friendly desktop metaphor interface
Usually mouse, keyboard, and monitor
Icons represent files, programs, actions, etc
Various mouse buttons over objects in the interface cause various actions (provide information, options, execute function, open directory (known as a folder)
Invented at Xerox PARC

61. User Operating System Interface - GUI
Many systems now include both CLI and GUI interfaces
Microsoft Windows is GUI with CLI “command” shell
Apple Mac OS X as “Aqua” GUI interface with UNIX kernel underneath and shells available
Solaris is CLI with optional GUI interfaces (Java Desktop, KDE)

63. Operating system structure Self Study

64. Simple Structure
Called “no structure”
The operating system is a collection of procedures, each of which call any of the other whenever it requires their needs.

65. Simple Structure
MS-DOS – written to provide the most functionality in the least space
Not divided into modules
Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated

66. MS-DOS Layer Structure

67. Traditional UNIX System Structure

68. Layered Approach
The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.
With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers

69. Layered Operating System

70. Microkernel System Structure
Philosophy of microkernel is to have the bare essentials in the kernel.
Removing all non-essential components from kernel and implement them in system-and -user level. Program thst results a smaller kernel called microkernal.

71. Solaris Modular Approach

72. Microkernel System Structure
Moves as much from the kernel into “user” space.
Communication takes place between user modules using message passing.
Benefits:
Easier to extend a microkernel
Easier to port the operating system to new architectures
More reliable (less code is running in kernel mode)
More secure

73. Break

74. The Process
Process

75. Process Concept An operating system executes a variety of programs:
Batch system – jobs
Time-shared systems – user programs or tasks
The terms job and process almost interchangeably

76. Process Concept A program in execution
An instance of a program running on a computer
The entity that can be assigned to and executed on a processor
A unit of activity characterized by the execution of a sequence of instructions, a current state, and an associated set of system instructions

77. Process Concept
Process – a program in execution; process execution must progress in sequential fashion

78. 1. An executable (i.e., code) 2. Associated data needed by
A process consists of
1. An executable (i.e., code)
2. Associated data needed by
the program (global data,
dynamic data, shared data)
3. Execution context (or state) of the program, e.g.,
Contents of data registers
Program counter, stack pointer
Memory allocation
Open file (pointers)

79. Process in Memory

80. Process Program : Passive entity (executable file)
Process: Active entity (progam counter specify next instruction).
A program becomes process when executable file is loaded into memory

81. Process State As a process executes, it changes state
new: The process is being created
running: Instructions are being executed
waiting: The process is waiting for some event to occur
ready: The process is waiting to be assigned to a processor
terminated: The process has finished execution

82. Diagram of Process State

83. Process Control Block (PCB)
Information associated with each process
Process state
Program counter
CPU registers
CPU scheduling information
Memory-management information
Accounting information
I/O status information

84. Process Control Block (PCB)

85. PROCESSES Process State PROCESS CONTROL BLOCK:
CONTAINS INFORMATION ASSOCIATED WITH EACH PROCESS:
It's a data structure holding:
PC, CPU registers,
memory management information,
accounting ( time used, ID, ... )
I/O status ( such as file resources ),
scheduling data ( relative priority, etc. )
Process State (so running, suspended, etc. is simply a field in the PCB ).
3: Processes

86. Example Execution

87. Trace of Process

88. CPU Switch From Process to Process