Operating System

CSE Sec-C
 Components of a computer
 The five main components that are:
1. A motherboard
2. A Central Processing Unit (CPU)
3. A Graphics Processing Unit (GPU), also known as a
video card
4. Random Access Memory (RAM), also known as
volatile memory
5. Storage: Solid State Drive (SSD) or Hard Disk Drive
(HDD)
1. Motherboard
 All components of a computer communicate
through a circuit board called the motherboard.
2. Central Processing Unit (CPU)
 It is Central Processing Unit of the computer. The control unit and
ALU are together known as CPU. CPU is the brain of computer
system.
 It performs following tasks:

I. It performs all operations.

II. It takes all decisions.
III. It controls all the units of computer.
Arithmetic Logic Unit (ALU)
 Data entered into computer is sent to RAM, from where it is
then sent to ALU, where rest of data processing takes place.
 All types of processing, such as comparisons, decision-
making and processing of non-numeric information takes
place here and once again data is moved to RAM.

Control Unit:
 Control unit performs following functions −

1. It controls all activities of computer

2. Supervises flow of data within CPU

3. Transfers data to Arithmetic and Logic Unit

4. Transfers results to memory

5. Fetches results from memory to output devices

3. Graphics Processing Unit (GPU):
 Graphics cards often communicate directly with the display
monitor.
4. Random Access Memory (RAM):
 RAM, also known as volatile memory, stores data regarding
frequently accessed programs and processes.
 It's called volatile memory because it gets erased every time
the computer restarts.
 RAM helps programs and games start up and close quickly.
5. Storage:
 All computers need somewhere to store their data. Modern computers
either use a Hard Disk Drive (HDD) or Solid State Drive (SSD).
 HDDs are made of an actual disk onto which data is stored. The disk is
read by a mechanical arm. (HDDs are cheaper than SSDs, but are slowly
becoming more and more obsolete.)
 SSDs (think SIM cards) have no moving parts and are faster than a hard
drive, because no time is spent waiting for a mechanical arm to find data
on a physical location on the disk.
 Introduction to Operating System (OS)
 An operating system acts as an intermediary between the
user of a computer and computer hardware.
 The purpose of an operating system is to provide an
environment in which a user can execute programs
conveniently and efficiently.
Types of operating systems
 The most common operating systems for personal computers
are Microsoft Windows, macOS, Linux and Android.
 Microsoft created the Windows operating system in the mid-
1980s. There have been many different versions of Windows, but
the most recent ones are Windows 10 (released in
2015), Windows 8 (2012), Windows 7 (2009), and Windows
Vista (2007).
 MacOS (previously called OS X) is a line of operating systems
created by Apple. It comes preloaded on all Macintosh computers,
or Macs. Some of the specific versions include Mojave (released
in 2018), High Sierra (2017), and Sierra (2016).
 Mobile operating systems include Apple iOS and Google
Android.
Where is the operating system stored on a computer?

 With most computers, the operating system is

stored on the primary hard drive inside the
computer.
Basic Components of OS:-
 Operating system provides basis for application programs
and acts as an intermediary between user & hardware.
Goals of the Operating System:-
 There are two types of goals of an Operating System i.e.
Primary Goals and Secondary Goal.

Primary Goal:
The primary goal of an Operating System is to provide a user-
friendly and convenient environment.
Secondary Goal:
The secondary goal of an Operating System is efficiency. The
Operating System should perform all the management of
resources in such a way that the resources are fully utilised.
Functions of an Operating System:-

1. Resource Management:

 In the case of server where multiple users wants to access

the system or hardware then it act as a resource manager.
 Manage the computer's resources, such as the central
processing unit, memory, disk drives, I/O devices and
printers.
 In which user how much space is required and which device
is required all this activities manages by OS.
2. Process Management:

 At a particular instant of time, the CPU may have a number

of processes that are in the ready state.
 But at a time, only one process can be processed by a
processor.
 So, the CPU should apply some kind of algorithm that can
be used to provide uniform and efficient access to resources
by the processes.
3. Storage Management (or) File Management:

 Data permanently store in hard disk i.e. managed by

operating system.
 This storage management done by file systems.
 Keeps track of information, location, uses, status etc. The
collective facilities are often known as file system.
4. Memory Management:

 For the execution of a process, the whole process is put into

the main memory and the process is executed and after the
execution of the process, the memory is freed and that
memory can be used for other processes.
 So, it is the duty of the Operating System to manage the
memory by allocating and deallocating the memory for the
process.
Other Functionalities such as

5. Security
Prevents unauthorized access to programs and data by means
of passwords and other similar techniques.
6. Job Accounting
Keeps track of time and resources used by various jobs and/or
users.
7. Error-detecting Aids
Production of error messages, and other debugging and error-
detecting methods.
 Basics of Operating System
 Some of basic knowledge of the structure of computer
system is required to understand how operating systems
work.
 Basics of Operating System

 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.
 Each device controller is in charge of a specific type of device.
 The CPU and the device controllers can execute concurrently,
competing for memory cycles.
 To ensure orderly access to the shared memory, a memory
controller is provided whose function is to synchronize access to
the memory.
Bootstrap program:

 The initial program that runs when a computer is powered

up or rebooted.
 It is stored in Read Only Memory (ROM).
 The bootstrap program must know how to load the OS and
to start executing that system.
Interrupt:
 An interrupt is a signal to the processor emitted by hardware
or software indicating an event that needs immediate
attention.
 The interrupts can be either hardware interrupts or software
interrupts.
 A hardware interrupt is an electronic alerting signal sent to
the processor from an external device. For example , when
we press a key on the keyboard or move the mouse, they
trigger hardware interrupts which cause the processor to
read the keystroke or mouse position.
 Hardware may trigger an interrupt at any time by sending a
signal to the CPU, usually by way of the system bus.
System Call (or) Monitor Call:-

 Software may trigger an interrupt by executing a special

operation called a system call (also called a monitor call).
 A hardware triggers then it is known as Interrupt & software
triggers means its known as system call.