lllllllllllllllllllllllllllllllllllllllllllllllllll

‫ﺑﺎﻹﺳﻛﻧدرﯾﺔ‬ ‫ﻓﺎروس‬ ‫ﺟﺎﻣﻌـــــــــــﺔ‬
Pharos University in Alexandria
CS 206 – Operating Systems
Level 2 - Semester 4 - Spring 2024
Lecture 01: Introduction to OS
Chapter 1

Computer system
What is an operating systems?
Operating system goals
What Operating Systems Do?
Kernel
Computer Startup
Computer-System Organization
Computer Architecture
Operating System Structure
Storage Structure
CS 206: Operating Systems
Soha A. Mohamed Lecture 01: Introduction to OS
Outline

Soha A. Mohamed
Computer system
• CPU, memory, I/O devices.
Hardware
• Controls and coordinates use of hardware among various
applications and users.
Operating system
• Ex. Word processors, compilers, web browsers, database
systems, video games.
Application programs
• People, machines, other computers.
Users

Soha A. Mohamed
Computer system

Soha A. Mohamed
An operating system is a program that manages a computer’s hardware. It also provides a
basis for application programs and acts as an intermediary between the computer user and
the computer hardware.
What is an operating systems?

Soha A. Mohamed

Soha A. Mohamed
 What is operating system?
a) collection of programs that manages hardware resources.
b) system service provider to the application programs.
c) interface between the hardware and application programs.
d) all of the mentioned

Soha A. Mohamed
Operating system goals
• Execute user programs and make solving user problems easier.
• Make the computer system convenient to use.
• Use the computer hardware in an efficient manner.

Soha A. Mohamed

Soha A. Mohamed
User View
 Users want convenience, ease of use and good
performance.
• Don’t care about resource utilization.
 In shared computer such as mainframe or
minicomputer must keep all users happy.

Soha A. Mohamed
System View
 From the computer’s point of view, the operating system is the program most
intimately involved with the hardware. In this context, we can view an operating
system as a resource allocator.
 A computer system has many resources that may be required to solve a problem:
• CPU time, memory space, file-storage space, I/O devices, and so on.
• The operating system acts as the manager of these resources.

Soha A. Mohamed
System View
 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.

Kernel
Kernel is the one
program running at all
times on the
computer.
 Which one of the following is not true?
a) kernel is the program that constitutes the central core of the operating system.
b) kernel is the first part of operating system to load into memory during booting.
c) kernel is made of various modules which can not be loaded in running operating
system.
d) kernel remains in the memory during the entire computer session.

Typically stored in ROM or electrically erasable programmable
read-only memory (EPROM), generally known as firmware.
Initializes all aspects of system.
Loads operating system kernel and starts execution.
Soha A. Mohamed
Computer Startup | Bootstrap program
Bootstrap program is loaded at power-up or reboot
Q1: What is the difference between firmware, software and hardware?

Soha A. Mohamed

Soha A. Mohamed
 PROM stands for “Programmable Read Only Memory“.
On this PROM, data can be written only one time, and it
remains there forever.
 When programmer writes programs on the PROM, then
this process is known as “Burning PROM”. After burning
data, you can’t make any modification in the burnt
content.

Soha A. Mohamed
 EPROM stands for “Erasable and Programmable Read
Only Memory”, and in which stored data can be deleted
by using of ultra-violet light.
 The ultraviolet light clears its data, and now ROM can be
reprogramed.
 Writing and erasing an EPROM, require a special device
called a PROM programmer or PROM burner.
https://youtu.be/2Trkapl2Hmo

Soha A. Mohamed
 EEPROM stands for “Electrically Erasable and
Programmable Read Only Memory“.
 In EEPROM, all activities such as programming and erasing
are performed by electrically.
 This EEPROM can be reprogrammed and erased in more
than ten thousand time.

Soha A. Mohamed
Q2: What is the difference between BIOS and CMOS?
CMOS (Complementary Metal Oxide Semiconductor) battery –
also called coin-cell battery.
CMOS (Complementary
Metal Oxide

Soha A. Mohamed
 BIOS is a firmware.
 BIOS stands for Basic Input/Output System. It's firmware that loads before your operating system.
 The BIOS performs start-up procedures that check system devices (ranging from your RAM to your
hard drive to your keyboard) and load your operating system.
https://www.youtube.com/watch?v=LGz0Io_dh_I
https://youtu.be/ncUmWthHrU0

Soha A. Mohamed
https://www.youtube.com/watch?v=LGz0Io_dh_I
https://youtu.be/ncUmWthHrU0
Legacy BIOS Unified Extensible Firmware Interface (UEFI).

Soha A. Mohamed
 CMOS battery powers your laptop's BIOS firmware, which is responsible for booting up your
computer and configuring data flow.
 CMOS (Complementary Metal Oxide Semiconductor) battery – also called coin-cell battery.

Soha A. Mohamed
Computer-System Organization
A modern general-purpose computer system consists of one or more CPUs and a number
of device controllers connected through a common bus that provides access to shared
memory.
Q3: What is GPU?
Q4: What is the difference between GPU and CPU?

Soha A. Mohamed
Single Processor System
Multiprocessor System

Soha A. Mohamed
https://youtu.be/6UEiQ9vUGWo

Soha A. Mohamed
Single processor vs multiprocessor systems
Single processor system contains only one processor while multiprocessor systems
contain two or more processors.
In Single processor system only one process can be executed at a time and then the
process is selected from the ready queue.
As in the diagram, there are multiple
applications that need to be executed.
However, the system contains a single
processor and only one process can
be executed at a time.

Throughput
 Throughput of Single Processor
Systems is less than
Multiprocessor Systems Because
each and every task is performed by
the same processor.
 Throughput of
Multiprocessor systems is
greater than single
processor systems.
Soha A. Mohamed
Advantages Multiprocessor system
 Multiprocessors system also known as parallel systems / tightly coupled
systems.
 Increased throughput: by increasing the number of processors, we expect
to get more work done in less time.
Throughput - Number of processes completed per unit time.

Cost
Economic
 Single Processor Systems cost
more because each processor
requires separate resources (Mass
Storage, Peripherals, Power Supplies
etc.).
 Multiprocessor Systems
cost less than equivalent
multiple single processor
systems because they uses
same resources on sharing
basis.
Soha A. Mohamed
systems.
 Economy of scale: Multiprocessor systems can cost less than equivalent
multiple single-processor systems.

Soha A. Mohamed
systems.
 Increased reliability: graceful degradation or fault tolerance.
Reliability
 Less reliable because failure in
one processor will result in failure of
entire system.
 More reliable because
failure of one processor
does not halt the entire
system but only speed will
be slow down.

Soha A. Mohamed
Types of multiprocessor system

Soha A. Mohamed
Multiprocessor system
Each processor is assigned a task. All processors perform all tasks.

Soha A. Mohamed
Multiprocessor system
 The three are
similar to each
other.
 All CPUs
participate in
performing these
task or processes
P1, P2, and P3.
 The three are similar
to each other.
 Asymmetric have a
master slave
approach.
 So, one of the CPU
and one of the
processor will act as
a master, and the
remaining
processors will be
slaves.
 If a CPU fails, the
master will take care
of how to distribute
the loads.
Asymmetric
Multiprocessing
Slave 3
P3
Master
Slave 2
P2
Slave 1
P1
Symmetric
Multiprocessing
CPU 1
CPU 2
CPU 3
P1
P2
P3

Soha A. Mohamed
Multicore processor
Q5: What is a multicore processor?
A processor with a single core is called a Unicore processor. But a processor
with two or more cores is called a multicore processor.

Soha A. Mohamed
Dual-Core Octa-Core
Quad-Core Hexa-Core
Multicore processor

Soha A. Mohamed
Multicore processor

Soha A. Mohamed
Multicore processor Vs Multiprocessor
Single Processor (single processor with multiple cores) Multi Processor (two or more processors)
Modern computers have multiple processors, and each processor has multiple cores present in it.

Soha A. Mohamed
Multicore processor Vs Multiprocessor

Single-user
Single-task
Single-user
Multi-task
Multi-user
Single-task
Multi-user
Multi-task
Soha A. Mohamed
Types of Operating Systems

Soha A. Mohamed

Soha A. Mohamed
 Network Operating Systems (NOS)

Soha A. Mohamed
 Q. What is Network Operating System (NOS)?
 Q. What is Distributed Operating System (DOS)?
 Q. What are the differences between NOS and DOS?
 Q. What are Real Time Operating Systems (RTOS)

Soha A. Mohamed
Multiprogramming
Multitasking

Soha A. Mohamed

Soha A. Mohamed
 Single tasking operating system was used before the multitasking operating
system. single tasking operating system allows user to perform a single task
at a time.
 So, tasks like printing a document or downloading an image from the
internet can be done one after another, leading to wastage of resources
which makes the operating system relatively slow and gives a bad user
experience.

Storage Structure
 Speed
 Cost
 Volatility
Q6: What is the different types of RAM?
Storage-Device Hierarchy

Storage Structure
 Registers (Processor register)
Registers are a type of computer memory built
directly into the processor or CPU (Central
Processing Unit) that is used to store and
manipulate data during the execution of
instructions.

Storage Structure
 Cache
Registers are a type of computer memory built
directly into the processor or CPU (Central
Processing Unit) that is used to store and
manipulate data during the execution of
instructions.
https://youtu.be/yi0FhRqDJfo

Storage Structure
 A byte is eight bits.
 A word is 2 bytes (16 bits).
 A doubleword is 4 bytes (32 bits).
 A quadword is 8 bytes (64 bits).
 Kilobyte, or KB, is 1,024 bytes
 Megabyte, or MB, is 1,0242 bytes
 Gigabyte, or GB, is 1,0243 bytes
 Terabyte, or TB, is 1,0244 bytes
 Petabyte, or PB, is 1,0245 bytes

Interrupt
 An interrupt is a signal emitted by
hardware or software.
 An interrupt is a signal sent from a device or from
software to the operating system.
 It causes the operating system to temporarily stop what
it's doing and service that

Interrupt
 An interrupt is a signal emitted by
hardware or software.
 Hardware may trigger an interrupt at any
time by sending a signal to the CPU,
usually by way of the system bus.
 Software may trigger an interrupt by
executing a special operation called a
system call (also called a monitor call).

System Call
 System call is made available by an operating system.
 There are two modes in which a program can be
executed: user mode and kernel mode.
 In user mode, program does not have direct access to
the memory, the hardware, and such resources.
 In kernel mode, then that program has the direct
access to the memory, the hardware, and such
resources.
 If a program is executing in kernel mode, then it is in a
privileged mode.

System Call
 But the problem is that when a program is executing in
a kernel mode and if that program happens to crash
during its execution, then the entire system would
crash, or it comes to a halt.
 But, if a program is executing in user mode, and if it
crashes, then the entire system does not crash or the
entire system does not come to a halt.
 So, user mode is a safer mode of operation.

System Call
 Most of the programs execute in user mode.
 When a program is executing in user mode and needs
access to some of the resources it makes a call to the
operating system (kernel) telling that it needs access
to certain resources.
 Then program is switched from user mode to kernel
mode to use those resources.
 When a program switches from user mode to kernel
mode (and vice versa) is known as context switching.

System Call
 System call is the programmatic way (routines written in C and C++) in which a
computer program requests a service from the kernel of the operating system.
1. We want to copy the contents of one file to
another file.
2. System call sequence for writing a simple
program to read data from one file and copy
them to another file.
Example

Types of System Call
Types of
System Calls
04
03
05
02
01
Device Management
Process Control
Information Maintenance
Communication
File Management

 Process Control
These types of system calls deal with process creation, process termination, process
allocation, deallocation etc.
 Create
 Terminate
 Load
 Execute
 End
 Abort
 Wait
 Alloate memory
 Deallocate

 Process Control
These types of system calls deal with process creation, process termination, process
allocation, deallocation etc.
1. fork(): Creates a new process (child) by duplicating the current process (parent).
2. exec(): Loads and runs a new program.
3. wait(): The primary purpose of this call is to ensure that the parent process doesn’t proceed
further with its execution until all its child processes have finished their execution. This call is
made when one or more child processes are forked.
4. exit(): It simply terminates the current process.
5. kill(): This call sends a signal to a specific process and has various purpose including –
requesting it to quit voluntarily, or force quit, or reload configuration.
The Linux System calls are fork(), exec(),
wait(), exit(), kill().

 File Management
File System Operations
These system calls are made while working with files in OS, File
manipulation operations such as creation, deletion, termination
etc.
 Open
 Close
 Create
 Delete
 Read
 Write
 Set attributes
 Get attributes

 File Management
File System Operations
These system calls are made while working with files in OS, File manipulation operations such as
creation, deletion, termination etc.
1. open(): Opens a file for reading or writing. A file could be of any type like text file, audio file etc.
2. read(): Reads data from a file. Just after the file is opened through open() system call, then if some
process want to read the data from a file, then it will make a read() system call.
3. write(): Writes data to a file. Whenever the user makes any kind of modification in a file and saves
it, that’s when this is called.
4. close(): Closes a previously opened file.
The Linux System calls are open(), read(),
write(), close().

 Device Management
0
 Request device
 Release device
 Read
 Write
 Set device attributes
 Get device attributes
 Attach device (logically)
 Detach device (logically)

 Device Management
The device management system calls are used to interact with various peripheral devices
attached to the PC or even the management of the current device.
1. ioctl(): Referred to as Input and Output Control, this call is made to set the mode of console
(input or output). It allows a process to control various console modes.
2. write(): It allows us to write data on console screen.
3. read(): It allows us to read data from console screen.
4. open(): This call is made whenever a device is opened. A unique file descriptor is created to
maintain the control access to the opened device.
5. close(): This call is made when the system or the user closes the device.
The Linux System calls are ioctl(), read(),
write(), open(), close().

 Information Maintenance
 Set process, file, or device attributes
 Get process, file, or device attributes
 Attach device (logically)
 Detach device (logically)
 Get (system / process) time or date
 Set (system / process) time or date

 Information Maintenance
getpid():
• getpid stands for Get the Process ID.
• The getpid() function shall return the process ID of the calling process.
• The getpid() function shall always be successful and no return value is reserved to
indicate an error.
alarm():
• This system call sets an alarm clock for the delivery of a signal that when it has to be
reached.
• It arranges for a signal to be delivered to the calling process.
sleep():
• This System call suspends the execution of the currently running process for some
interval of time.
• Meanwhile, during this interval, another process is given chance to execute.
The Linux System calls are getpid(),
alarm(), sleep().

01
 Create communication
 Delete Communication
02
 Send message
 Receive message
03
 Attach remote device
 Detach remote device
03
 Transfer status
information
 Communication

 Communication
When two or more process are required to communicate, then various IPC mechanism are used by the OS
which involves making numerous system calls. Some of them are:
pipe(): Creates a unidirectional communication channel between processes. For example, a parent process may
communicate to its child process through a pipe making a parent process as input source of its child process.
socket(): Creates a network socket for communication. Processes in same or other networks can communicate
through this socket.
shmget(): It is short for – ‘shared-memory-get’. It allows one or more processes to share a portion of memory and
achieve interprocess communication.
semget(): It is short for – ‘semaphore-get’. This call typically manages the coordination of multiple processes
while accessing a shared resource that is, the critical section.
msgget(): It is short for – ‘message-get’. IPC mechanism has one of the fundamental concept called – ‘message
queue’ which is a queue data structure inside memory through which various processes communicate with each
other. This message queue is allocated through this call allowing other processes a structured way of
communication for data exchange purpose.
The Linux System calls are pipe(),
shmget(), semget(), msgget().

Soha A. Mohamed
Q1: What is the difference between firmware, software and hardware?
Q5: What is a multicore processor?
Q3: What is GPU?
Q4: What is the difference between GPU and CPU?
Q2: What is the difference between BIOS and CMOS?
Questions – Presentations (1)
Q7: What is the Difference Between Multicore and Multiprocessor?
Q6: What is the different types of RAM?

 Q8. What is Network Operating System (NOS)?
 Q9. What is Distributed Operating System (DOS)?
 Q10. What are the differences between NOS and DOS?
 Q11. What are Real Time Operating Systems (RTOS)?
 Q12. Create 50 MCQ (with answers) concerning this lecture.
 Q13. Create 50  and  (with answers) concerning this lecture.
 Q14. Discuss Linux system call in Detail
Soha A. Mohamed

 Q15. Think about (minimum) 10 OS projects.
Soha A. Mohamed

Thank You
Chapter 1
https://codex.cs.yale.edu/avi/os-book/OS9/practice-exer-
dir/index.html

lllllllllllllllllllllllllllllllllllllllllllllllllll

More Related Content

Similar to lllllllllllllllllllllllllllllllllllllllllllllllllll (20)

Recently uploaded (20)

lllllllllllllllllllllllllllllllllllllllllllllllllll