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Introduction to Operating

System (OS)

Course Content:

• (^) What is an OS.
• (^) What are its key functions.
• (^) The evaluation of OS.
• (^) What are the popular types of OS.
• (^) Basics of UNIX and Windows.
• (^) Advantages of open source OS like Linux.
• (^) Networks OS.

The Structure of Computer Systems

 Accessing computer resources is divided into layers.

 Each layer is isolated and only interacts directly with the layer below or above

it.

 If we install a new hardware device

 No need to change anything about the user/applications.

 However, you do need to make changes to the operating system.

 You need to install the device drivers that the operating system will use to

control the new device.

 If we install a new software application

 No need to make any changes to your hardware.

 But we need to make sure the application is supported by the operating

system

 user will need to learn how to use the new application.

 If we change the operating system

 Need to make sure that both applications and hardware will compatible

with the new operating system.

Computer

Architecture

Special busses (roads) connecting

all input/output devices to

motherboard.

RAM – Random Access Memory

 This is like a desk, or a workspace, where your computer temporarily stores all of

the information (data) and instructions (software or program code) that it is

currently using.

 Each RAM chip contains millions of address spaces.

 Each address space is the same size, and has its own unique identifying number

(address).

 The operating system provides the rules for using these memory spaces, and

controls storage and retrieval of information from RAM.

 Device drivers for RAM chips are included with the operating system.

Operating System Mode

 The User Mode is concerned with the actual

interface between the user and the system.

 It controls things like running applications

and accessing files.

 The Kernel Mode is concerned with everything

running in the background.

 It controls things like accessing system

resources, controlling hardware functions and

processing program instructions.

 System calls are used to change

mode from User to Kernel.

Kernel cont…

 Kernel includes:-

1. Scheduler: It allocates the Kernel’s processing time to various

processes.

2. Supervisor: It grants permission to use computer system

resources to each process.

3. Interrupt handler : It handles all requests from the various

hardware devices which compete for kernel services.

4. Memory manager : allocates space in memory for all users of

kernel service.

 kernel provides services for process management, file

management, I/O management, memory management.

 System calls are used to provide these type of services.

System Call

System call is the programmatic way in which a computer

program/user application requests a service from the kernel of the

operating system on which it is executed.

Application program is just a user-process. Due to security reasons ,

user applications are not given access to privileged resources(the ones

controlled by OS).

When they need to do any I/O or have some more memory or spawn a

process or wait for signal/interrupt, it requests operating system to

facilitate all these. This request is made through System Call.

System calls are also called software-interrupts.

BIOS

• (^) BIOS firmware was stored in a ROM/EPROM (Erasable Programmable

Read-Only Memory) chip known as firmware on the PC motherboard.

• (^) BIOS can be accessed during the initial phases of the boot procedure by

pressing del, F2 or F10.

• (^) Finally, the firmware code cycles through all storage devices and looks

for a boot-loader. (usually located in first sector of a disk which is 512

bytes)

• (^) If the boot-loader is found, then the firmware hands over control of the

computer to it.

UEFI

• UEFI stands for Unified Extensible Firmware Interface. It does the same job as a BIOS, but

with one basic difference: it stores all data about initialization and startup in an .efi file,

instead of storing it on the firmware.

• (^) This .efi file is stored on a special partition called EFI System Partition (ESP) on the hard disk.

This ESP partition also contains the bootloader.

• (^) UEFI was designed to overcome many limitations of the old BIOS, including:

 UEFI supports drive sizes upto 9 zettabytes, whereas BIOS only supports 2.2 terabytes.

 UEFI provides faster boot time.

 UEFI has discrete driver support, while BIOS has drive support stored in its ROM, so updating BIOS

firmware is a bit difficult.

 UEFI offers security like "Secure Boot", which prevents the computer from booting from

unauthorized/unsigned applications. This helps in preventing rootkits.

 UEFI runs in 32bit or 64bit mode, whereas BIOS runs in 16bit mode. So UEFI is able to provide a GUI

(navigation with mouse) as opposed to BIOS which allows navigation only using the keyboard.

1. Process Management

• A process is a program in execution.
• (^) A process needs certain resources, including CPU time, memory, files, and I/O devices to

accomplish its task.

• (^) Simultaneous execution leads to multiple processes. Hence creation, execution and

termination of a process are the most basic functionality of an OS

• (^) If processes are dependent, than they may try to share same resources. thus task of process

synchronization comes to the picture.

• (^) If processes are independent, than a due care needs to be taken to avoid their overlapping

in memory area.

• (^) Based on priority, it is important to allow more important processes to execute first than

others.

2. Memory management
   • Memory is a large array of words or bytes, each with its own address.
   • (^) It is a repository of quickly accessible data shared by the CPU and I/O devices.
   • (^) Main memory is a volatile storage device. When the computer made turn off everything

stored in RAM will be erased automatically.

• (^) In addition to the physical RAM installed in your computer, most modern operating systems

allow your computer to use a virtual memory system. Virtual memory allows your computer

to use part of a permanent storage device (such as a hard disk) as extra memory.

• (^) The operating system is responsible for the following activities in connections with memory

management:

 Keep track of which parts of memory are currently being used and by whom.

 Decide which processes to load when memory space becomes available.

 Allocate and de-allocate memory space as needed.

4. Device Management or I/O Management

• (^) Device controllers are components on the motherboard (or on expansion cards) that act as an

interface between the CPU and the actual device.

• Device drivers, which are the operating system software components that interact with the devices

controllers.

• (^) A special device (inside CPU) called the Interrupt Controller handles the task of receiving interrupt

requests and prioritizes them to be forwarded to the processor.

• (^) Deadlocks can occur when two (or more) processes have control of different I/O resources that are

needed by the other processes, and they are unwilling to give up control of the device.

• (^) It performs the following activities for device management.

 Keeps tracks of all devices connected to system.

 Designates a program responsible for every device known as Input/output controller.

 Decides which process gets access to a certain device and for how long.

 Allocates devices in an effective and efficient way.

 Deallocates devices when they are no longer required.

5. Security & Protection

• (^) The operating system uses password protection to protect user data

and similar other techniques.

• (^) It also prevents unauthorized access to programs and user data by

assigning access right permission to files and directories.

• (^) The owners of information stored in a multiuser or networked

computer system may want to control use of that information,

concurrent processes should not interfere with each other.