Operating System (OS) Notes

Introduction to operating System

Definition Operating System (OS)-

An Operating System is a software that acts as an interface between computer hardware components and the user. Every computer system must have at least one operating system to run other programs. Applications like Browsers, MS access, MS Office, Notepad Games, etc., need some environment to run and perform its tasks.

In other word we can say that An operating system is a set of programs that control the execution of application programs and act as an intermediary between a user of a computer and the computer hardware. OS is software that manages the computer hardware as well as providing an environment for application programs to run.

The OS helps us to communicate with the computer without knowing how to speak the computer’s language. It is not possible for the user to use any computer or mobile device without having an operating system.

Examples - Android, Windows, Windows/NT, OS/2 and MacOS, Linux, Unix etc.

Operating system Objective-

(1)  To make the computer system convenient and easy to use for the user.

(2)  To use the computer hardware in an efficient way.

(3)  To execute user programs and make solving user problems easier.

Indexing of Operating system-

1. Definition of Operating System

2. History Of Operating System (OS)

3. Examples of Operating System

4. Types of Operating System (OS)

5. Functions of Operating System.

6. Features of Operating System (OS)

7. Advantage of Operating System

8. Disadvantages of Operating System

9. What is Kernel in Operating System ?

10. Features of Kernel

11. Types of Kernel.

12. Difference between Firmware and Operating System

13. Difference between 32-Bit and 64-Bit Operating System

1. Definition of Operating System / What is OS ?

An operating system is a set of programs that control the execution of application programs and act as an intermediary between a user of a computer and the computer hardware. OS is software that manages the computer hardware as well as providing an environment for application programs to run.

2. History Of Operating System (OS)-

1. Operating systems were first developed in the late 1950's to manage tape storage

2. The General Motors Research Lab implemented the first OS in the early 1950s for their IBM 701

3. In the mid-1960's, operating systems started to use disks

4. In the late 1960's, the first version of the Unix OS was developed

5. The first OS built by Microsoft was DOS. It was built in 1981s by purchasing the 86-DOS software from a Seattle company

6. The present-day popular Windows OS first came to existence in 1985s when a GUI was created and paired with MS-DOS and Windows OS.

7. The present-day popular Android OS for mobile devices.

3. Examples of Operating System OS-

The Operating System OS examples with the Market Shares.

Windows=40.34%, Android=37.95%, IOS=15.44%, Mac OS=4.34%, Chrome OS=0.14%, Linux=0.95%, WindowS_Phone OS=0.06%, etc.

4.Categories /Types of Operating System (OS)-

Following are giving the popular types of Operating System OS:

• Batch Operating System

• Multitasking/Time Sharing OS

• Multiprocessing OS

• Real Time OS

• Distributed OS

• Network OS

• Mobile OS

Performance development of OS

1. On-line and off-line operation

A special subroutine was written for each I/O device called a device controller. Some I/O devices has been equipped for either on-line operation (they are connected to the processor), or off-line operations (they are run by control unit).

2.     Buffering

A buffer is an area of primary storage for holding data during I/O transfer. On input, the data are placed in the buffer by an I/O channel, when the transfer is complete the data may be accessed the processor. The buffing may be single or double.

3.     Spooling (Simultaneously Peripheral Operation On-Line)

Spooling uses the disk as a very large buffer. Spooling is useful because device access data that different rates. The buffer provides a waiting station where data can rest while the slower device catches up.

Spooling allows overlapping between the computation of one job and I/O of another job.

1.   Multiprogramming

In multiprogramming several programs are kept in main memory at the same time, and the CPU is switching between them , thus the CPU always has a program to be execute. The OS begins to execute one program from memory, if this program need wait such as an I/O operation, the OS switches to another program. Multiprogramming increases CPU utilization. Multiprogramming system provide an environment in which the various system resources are utilized effectively, but they do not provide for user interaction with the computer system.

Advantages

a)  High CPU utilization.

b) It appears   that   many   programs   are   allotted   CPU   almost simultaneously.

Disadvantages

a)     CPU scheduling is requires.

b) To accommodate many jobs in memory, memory management is required.

2.   Parallel system

There are more than on processor in the system. These processors share the computer bus, clock, memory and I/O devices.

The advantage is to increase throughput (the number of programs completed in time unit)

3.   Distributed system

Distribute the computation among several physical processors. It involves connecting 2 or more independent computer systems via communication link. So, each processor has its own O.S. and local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines. 

Advantages of distributed systems:

a)   Resources Sharing – You can share files and printers.

b)  Computation speed up – A job can be partitioned so that each processor can do a portion concurrently (load sharing).

c)   Reliability – If one processor failed the rest still can function with no problem.

d)  Communications – Such as electronic mail, ftp

4.   Personal computer

Personal computers – computer system dedicated to a single user. PC operating systems were neither multi-user nor multi-tasking. The goal of PC operating systems were to maximize user convenience and responsiveness instead of maximizing CPU and I/O utilization.

•Examples: Microsoft Windows and Apple Macintosh

• Batch Operating System

  • • Some computer processes are very lengthy and time-consuming. To speed the same process, a job with a similar type of needs are batched together and run as a group.

    • The user of a batch operating system never directly interacts with the computer. In this type of OS, every user prepares his or her job on an offline device like a punch card and submit it to the computer operator.

    • In this type of OS, users submit jobs on regular schedule (e.g. daily, weekly, monthly) to a central place where the user of such system did not interact directly with computer system. To speed up the processing, jobs with similar needs were batched together and were run through the computer as a group. Thus, the programmer would leave the programs with the operator. The output from each job would send to the appropriate programmer. The major task of this type was to transfer control automatically from one job to the next.

    • Disadvantages of Batch System

Turnaround time can be large from user standpoint.

Difficult to debug program.

• Multi-Tasking/Time-sharing Operating systems

  • • Time-sharing operating system enables people located at a different terminal(shell) to use a single computer system at the same time. The processor time (CPU) which is shared among multiple users is termed as time sharing.

• Real time OS operating system

  • • A real time operating system time interval to process and respond to inputs is very small. Examples: Military Software Systems, Space Software Systems are the Real time OS example.

    • This type of OS provides on-line communication between the user and the system, the user gives his instructions directly and receives intermediate response, and therefore it called interactive system.

    • The time sharing system allows many user simultaneously share the computer system. The CPU is multiplexed rapidly among several programs, which are kept in memory and on disk. A program swapped in and out of memory to the disk.

    • Time sharing system reduces the CPU ideal time. The disadvantage is more complex.

    • Real Time System is characterized by supplying immediate response. It guarantees that critical tasks complete on time. This type must have a pre- known maximum time limit for each of the functions to be performed on the computer. Real-time systems are used when there are rigid time requirements on the operation of a processor or the flow of data and real-time systems can be used as a control device in a dedicated application.

    • The airline reservation system is an example of this type.

• Distributed Operating System

  • • Distributed systems use many processors located in different machines to provide very fast computation to its users.

• Network Operating System

  • Network Operating System runs on a server. It provides the capability to serve to manage data, user, groups, security, application, and other networking functions.

• Mobile OS

  • Mobile operating systems are those OS which is especially that are designed to power smartphones, tablets, and wearables devices.

  • Some most famous mobile operating systems are Android and iOS, but others include BlackBerry, Web, and smart watch OS.

4.Functions of Operating System-

Some typical operating system OS functions may include managing memory, files, processes, I/O system and devices, security, etc.

In an OS operating system software performs each of the function:

1. Process management: Process management helps OS to create and delete processes. It also provides mechanisms for synchronization and communication among processes.

2. Memory management: Memory management module performs the task of allocation and de-allocation of memory space to programs in need of this resources.

3. File management: It manages all the file-related activities such as organization storage, retrieval, naming, sharing, and protection of files.

4. Device Management: Device management keeps tracks of all devices. This module also responsible for this task is known as the I/O controller. It also performs the task of allocation and de-allocation of the devices.

5. I/O System Management: One of the main objects of any OS is to hide the peculiarities of that hardware devices from the user.

6. Secondary-Storage Management: Systems have several levels of storage which includes primary storage, secondary storage, and cache storage. Instructions and data must be stored in primary storage or cache so that a running program can reference it.

7 Security: Security module protects the data and information of a computer system against malware threat and authorized access.

8. Command interpretation: This module is interpreting commands given by the and acting system resources to process that commands.

9. Implementing user interface.

10. Networking: A distributed system is a group of processors which do not share memory, hardware devices, or a clock. The processors communicate with one another through the network.

11.Job accounting: Keeping track of time & resource used by various job and users.

12.Communication management: Coordination and assignment of compilers, interpreters, and another software resource of the various users of the computer systems.

1.  Facilitating parallel operations.

2.  Organizing data for secure and rapid access.

.3.   Handling network communications.

4. Preventing users from interfering with one another

5.     Scheduling resource among users.

6. Facilitating I/O operations.

7. Recovering from errors.

8. Accounting for resource storage.

9.     Sharing HW among users.

10.   Allowing users to share data among themselves.

Below are the main functions of Operating System:

Features of Operating System (OS)-

Here is a list important features of Oprating system OS:

• Protected and supervisor mode

• Allows disk access and file systems Device drivers Networking Security

• Program Execution

• Memory management Virtual Memory Multitasking

• Handling I/O operations

• Manipulation of the file system

• Error Detection and handling

• Resource allocation

• Information and Resource Protection

Advantage of Operating System

• The operating system must make sure that the computer system convenient to use

• Operating System acts as an intermediary among applications and the hardware components

• Easy to use with a GUI 

• Offers an environment in which a user may execute programs/applications.

• It provides the computer system resources with easy to use format.

• Acts as an intermediator between all hardware’s and software’s of the system.

• Allows you to hide details of hardware by creating an abstraction.

Disadvantages of Operating System-

• Operating system’s software is quite expensive for small size organization which adds burden on them. Example Windows xp,98,7, 8, 8.1, 10..

• If any issue occurs in OS Operating System , you may lose all the contents which have been stored in your system

• It is never entirely secure as a threat can occur at any time.

Core OS Operating Systems-

What is Kernel in OS Operating Systems?

The kernel is the central component of a computer operating systems. The only job performed by the kernel is to the manage the communication between the software and the hardware. A Kernel is at the nucleus of a computer. It makes the communication between the hardware and software possible. While the Kernel is the innermost part of an operating system, a shell is the outermost one.

Features of Kernel

• Low-level scheduling of processes

• Context switching 

• Core OS operating systems

• Inter-process communication

• Process synchronization

Types of Kernel

There are many types of kernels that exists, but among them, given below two most popular kernels are:

1. Monolithic

A monolithic kernel is a single code or block of the program. It provides all the required services offered by the operating system. It is a simplistic design which creates a distinct communication layer between the hardware and software.

2. Microkernels

Microkernel manages all system resources. In this type of kernel, services are implemented in different address space. The user services are stored in user address space, and kernel services are stored under kernel address space. So, it helps to reduce the size of both the kernel and operating system.

Difference between Firmware and Operating Systems-

• Define Firmware: Firmware is one kind of programming that is embedded on a chip in the device which controls that specific device.

• Define Operating System: OS provides functionality over and above that which is provided by the firmware.

• Firmware It is stored on non-volatile memory.

• OS is stored on the hard drive.

• Firmware is programs that been encoded by the manufacture of the IC or something and cannot be changed.

• OS is a program that can be installed by the user and can be changed.

Difference between 32-Bit and 64-Bit Operating Systems-

• Architecture and Software

Allow 32 bit of data processing simultaneously

Allow 64 bit of data processing simultaneously

• Compatibility

32-bit applications require 32-bit OS and CPUs.

64-bit applications require a 64-bit OS and CPU.

• Systems Available

All versions of Windows 8, Windows 7, Windows Vista, and Windows XP, Linux, etc.

Windows XP Professional, Vista, 7, Mac OS X and Linux.

• Memory Limits

32-bit systems are limited to 3.2 GB of RAM.

64-bit systems allow a maximum 17 Billion GB of RAM.

Need for an OS:

The primary need for the OS arises from the fact that user needs to be provided with services and OS ought to facilitate the provisioning of these services. The central part of a computer system is a processing engine called CPU. A system should make it possible for a user’s application to use the processing unit. A user application would need to store information. The OS makes memory available to an application when required. Similarly, user applications need use of input facility to communicate with the application. This is often in the form of a key board, or a mouse or even a joy stick (if the application is a game for instance).

OS Operating systems Summary-

• Operating System (or shortly OS) primarily provides services for running applications on a computer system.

• What is OS (Operating System definition) and its Types: An operating system is a software which acts as an interface between the end user and. computer hardware. Different categories of Operating System in computer and other devices are: Batch Operating System, Multitasking/Time Sharing OS, Multiprocessing OS, Real Time OS, Distributed OS, Network OS & Mobile OS.

• The kernel is the central component of a computer operating systems. The only job performed by the kernel is to the manage the communication between the software and the hardware

• Two most popular kernels are Monolithic and MicroKernels

• Process, Device, File, I/O, Secondary-Storage, Memory management are various functions of an Operating System.

• Personal Computer Operating Systems were first developed in the late 1950s to manage tape storage

• Explain Operating System working: OS works as an intermediate between the user and computer. It helps the user to communicate with the computer without knowing how to speak the computer’s language.