BCA SEM-2 SUB : Operating system, Cheat Sheet of Computer Fundamentals

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Subject:303 Operating System

Unit-1: Basic concept of an operating system

1. Definition and Function of operating systems.

2. Evolution of operating system: Batch system, Multi programmed system,

time sharing and PCs.

3. Introduction to basic terms & batch processing system: Jobs, Processes files,

command interpreter.

4. Different types of operating system-real time systems, parallel. distributed

system.

5. Operating system structure-monolithic layered, virtual machine & Client

server.

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 What is booting Process in OS? Booting: When we start our Computer then there is an operation which is performed automatically by the Computer which is also called as Booting. In the Booting. System will check all the hardware's and Software's those are installed or Attached with the System and this will also load all the Files those are needed for running a system. In the Booting Process all the Files those are Stored into the ROM Chip will also be Loaded for Running the System. In the Booting Process the System will read all the information from the Files those are Stored into the ROM Chip and the ROM chip will read all the instructions those are Stored into these Files  There are two Types of Booting

1. Warm Booting: when the System Starts from the Starting or from initial State Means when we Starts our System this is called as warm Booting. In the Warm Booting the System will be Started from its beginning State means first of all, the user will press the Power Button, then this will read all the instructions from the ROM and the Operating System will b Automatically gets loaded into the System. 2. Cold Booting: The Cold Booting is that in which System Automatically Starts when we are Running the System, For Example due to Light Fluctuation the system will Automatically Restarts So that in this Chances Damaging of system are More, and the System will no be start from its initial State So May Some Files will b Damaged because they are not Properly Stored into the System.  Function Of Operating System: An operating system is a piece of software that manages the allocation of computer hardware. The coordination of the hardware must be appropriate to ensure the correct working of the computer system and to prevent user programs from interfering with the proper working of the system. Major Functions of Operating System:

1. Memory management: It manages both the primary and secondary memory has RAM, ROM, hard disk, pen drive etc. it checks and decides the allocation of memory space to different processes. When a user interacts with a system, the CPU is supposed to read or write operations, in this case, OS decides the amount of memory to be allocated for loading the program instructions and data into RAM. After this program is terminated, the memory area is again free and is ready to be allocated to other programs by the OS.
2. Processor Management: it facilitates processor management where it decides the order for the processes to access the processor as well as decides the processing time to be allocated for each process. Besides this, it monitors the status of processes, frees the processor when a process is executed then allocates it to a new process.

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3. Device/Hardware management: The operating system also contains drivers to

manage devices. A driver is a type of translation software that allows the operating system to communicate with devices, and there are different drivers for different devices as each device speaks a different language.

4. Run software applications: It offers the environment to run or use software

applications developed to perform specific tasks, for ex. Ms Word, Ms Excel, Photoshop, etc.

5. Data management: It helps in data management by offering and displaying directories for

data management. You can view and manipulate files, folders, e.g., You can move, copy, name, or rename, delete a file or a folder.

6. Evaluates the system’s health: It gives us an idea about the performance of the

hardware of the system. e.g., you can see how busy the CPU is, how fast the data is retrieved from the hard disk, etc.

7. Provide user interface: It acts as an interface between the user and the hardware. It can

be a GUI where you can see and click elements on the screen to perform various tasks. It enables you to communicate with the computer even without knowing the computer’s language.

8. I/O management: It manages the input output devices and makes the I/O process smooth

and effective. For example, It receives the input provided by the user through an input device and stores it in the main memory. Then it directs the CPU to process this input and accordingly provides the output through an output device such as a monitor.

9. Security: It has a security modules to protect the data or information stored in the memories

of the computer against malware and unauthorized access. Thus, it noy only manages your data but also helps to protect it.

10. Time Management: It helps CPU in time management. The Kernel OS keeps checking the

frequency of processes that requests CPU time. When two or more processes that are equally important compete for the CPU time, then the CPU time is sliced into segments and allocated to these processes in a round-robin fashion to prevent a single process from monopolizing the CPU.

11. Deadlock Prevention: OS also responds to interrupts, which are signals generated by a

program or a device to seek the attention of the CPU. The OS checks the priority of the interrupt, and if it is more important than the currently running process, it stops the execution of the current process and preserves this state of CPU then executes the requested process. Thereafter the CPU returns to the same state where it was stopped.

 Types of Operating System:

Some widely used operating systems are as follow: i. Batch Operating System ii. Multi-Programmed Operating System iii. Time Sharing Operating System iv. Desktop Operating System

i. Batch Operating System

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 In this execution environment, the CPU is often idle because the speed of the mechanical I/O devices are intrinsically slower than are those of electronics devices. ii. Multi Programmed Operating System  The most important aspect of job scheduling is the ability to multiprogramming. A single user cannot, in general, keep either the CPU or the I/O devices busy at all times.  Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute.  The operating system keeps several jobs or task in memory simultaneously given in following figure. This set of jobs is a subset of the jobs kept in the pool – because the number of jobs that can be kept simultaneously in memory is usually much smaller than the number of jobs that can be in the job pool. The operating system picks and begins to execute one of the jobs in the memory.  Eventually the job may have to wait for some task, such as an I/O operations, to complete. In a non-multiprogramming system, the CPU would sit an idle. In Multiprogramming System, the operating system simply switches to and executes another job.  When that job needs to wait, the CPU is switched to another job and so on.,  Eventually the first job finishes waiting and gets the CPU back. As long as at least one job needs to execute, the CPU is never sit an idle.  This idea is common in other life example. A lawyer does not work for only one client at a time. While one case is waiting to go to trial or have papers typed, the lawyer can work on  another case. If He/She has an enough clients, the lawyer will never be idle for lack of work.

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 Multiprogramming is the first example where the operating system must make decisions for the users. Multiprogramming operating systems are therefore fairly sophisticated.  All the the jobs or task that enter the system are kept in the job pool. This pool consists of all processes residing on disk awaiting allocation of main memory. if several jobs are ready to be brought into memory and if is not enough room for all of them then the system must choose among them. Making this decision is job scheduling.  If several jobs are ready to run at the same time, the system must choose among them. Making this decision is CPU scheduling.  Finally, multiple jobs running concurrently require that their ability to affect one another be limited in all phases of the operating system, including process scheduling, disk storage and memory management. iii. Time Sharing Systems or Multitasking Operating System  Time sharing or multitasking is a logical extension of multiple programming. The CPU executes multiple jobs by switching among them but the switches occur so frequently that the users can interact with each program which it is running.  A time shared operating system allows many users to share the computer simultaneously. Since each action or command in a time shared system tends to be short only a little CPU time is needed for each user.  As the system switch rapidly from one user to the next, each user is given the impression that the entire computer system is dedicated to his/her use, even though it is being shared among many users.  A time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time shared computer. Each user has at least one

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the design decisions made in operating systems for mainframes may not be appropriate for smaller systems. Personal Computer Definition: The first general-purpose, cost-effective personal computer created by IBM was called the IBM PC or means "personal computer". It is a microprocessor technology that has been any small, relatively inexpensive computer designed to be used by one person, at home or in an office. It is often simply called a Personal Computer (PC). The example of Personal Computer or PC are microcomputer, desktop computer, laptop computer, tablet. In all these computer manufacturers to put an entire CPU on one chip  Advantages of Operating System

1. User Friendly The interface provided by the GUI is much more user friendly compared to a command line interface. It comes with various symbols, buttons, menus and other graphical representations all which makes them easily understandable. As a result, users can interact and communicate with the machine easily. 2. Security It is a responsibility of an operating system to make sure each data present inside them is secure. They do this by encrypting data bit to bit. And most of the operating systems comes with a security program pre-installed. For an example, Windows contains its own security feature known as Windows Defender that actively removes malwares and other malicious files. For this purpose, users can use their own anti-malware software too. 3. Sharing Resources Operating system also provides the opportunity to share resources with other users. Such resources include, printers, fax machines, modems and players. Apart from that, operating system allows the transmission of various files such as videos, Images and apps with the connected devices. And also, if the data needs to be sent between multiple users, the users can use the email service. 4. Hardware Accessibility

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Graphical user interface allows users to access hardware functionality instantly in operating system. Unlike in command line interface, users don't need to write lines of codes for accessing hardware.

5. Multitasking Multitasking is another important feature of an operating system. Using operating system, users can perform different tasks simultaneously. There is no need to close one window to open another.  **Disadvantages of Operating System

1. Cost** Unless it is an open source operating system, generally all other platforms are considered to be expensive. Even though, users can choose the option of free operating system, it is not always the best since it does not possess all the features. If the operating system includes GUI functionality, it increases the cost even more. 2. Reliability An operating system is a vital software for any computer. Without an operating system, the computer cannot work. Therefore, any kind of failures in the operating system will result in affecting the entire computer. This in essence means that the processor will stop processing the data and other hardware components will not be working anymore. 3. Virus Attacks The risk of viruses is always higher in an operating system. Sometimes users can unknowingly download malicious programs, visit malicious websites or open virus containing email attachments all which can make a computer vulnerable to viruses.  **Different Types Of Operating Systems
2. Distributed Operating System:** Distributed system depend on networking for their functionality. Distributed systems are able to share computational tasks and provide a rich set of features to users.

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 Parallel Operating System or Multiprocessor Operating System:  Multiprocessor Systems also known as parallel system or tightly coupled systems are growing in importance. Such systems have more than one processor in close communication, sharing the computer bus, the clock and sometimes memory and peripheral devices.  The most common multiple processor systems now use SMP (Symmetric multiprocessing) in which each processor runs an identical copy of the operating system and these copies communicate with one another as needed.  Some Systems use asymmetric multiprocessing in which each processor is assigned a specific task. A master processor controls the system; the other processors either look to the master for instruction or have predefined tasks. This schemes defines a master-slave relationship. The master processor schedules and allocates work to the slave processors.  SMP means that all processors are peers; no master-slave relationship exists between processors. Each processor concurrently runs a copy of the operating system.  The difference between symmetric and asymmetric multiprocessing may be the result of either hardware or software. Special hardware can differentiate the multiple processors or the software can be written to allow only one master and multiple slaves.  As microprocessors become less expensive and more powerful, additional operating system functions are off-loaded to slave processors or back-ends For example, it is fairly easy to add a microprocessor with its own memory to manage a disk system. The microprocessor could receive a sequence of requests from the main CPU and implement its own disk queue and scheduling algorithm. This arrangement relieves the main CPU of the overhead of disk scheduling PCs contain a microprocessor in the keyboard to convert the keystrokes into codes to be sent to the CPU. Example of Multiprocessor Operating Systems are Windows OS, macOS and Linux.

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Multiprocessor systems have three main advantages

1. Increased throughput: We get more work done in less time by increasing the number of processors. When multiple processors cooperate on a task, a certain amount of overhead is incurred in keeping all the parts working correctly. This overhead, plus contention for shared resources, lowers the expected gain from additional processors.
2. Economy of Scale: Multiprocessor systems can save more money than multiple single-processor systems because they can share peripherals, mass storage and power supplies. If several programs operate on the same set of data, it is cheaper to store those data on one disk and to have all the processors share them than to have many computers with local disks and many copies of the data.
3. Increased Reliability: If functions can be distributed properly among several processors then the failure of one processor will not halt the system only slow it down. If we have ten processors and one fails, then each of the remaining nine processors must pick up a share of the work of the failed processor. Thus, the entire system runs only 10 percent slower rather than failing altogether. This ability to continue providing service proportional to the level of surviving hardware is called graceful degradation. Systems designed for graceful degradation are called fault tolerant.  Real Time Operating System: It is developed for real-time applications where data should be processed in a fixed, small duration of time. It is used in an environment where multiple processes are supposed to be accepted and processed in a short time. RTOS requires quick input and immediate response, e.g., in a petroleum refinery, if the temperate gets high and crosses the threshold value, there should be an immediate response to this situation to avoid the explosion. Similarly, this system is used to control scientific instruments, missile launch systems, traffic lights control systems, air traffic control systems, industrial control systems and certain display systems are real time systems etc.

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6. Memory is allocated appropriately Disadvantages of real-time operating system
7. A fewer number of tasks can run simultaneously to avoid errors.
8. It is not easy for a designer to write complex and difficult algorithms or proficient programs required to get the desired output.
9. Specific drivers and interrupt signals are required to respond to interrupts quickly.
10. It may be very expensive due to the involvement of the resources required to work.  Operating system structure: Operating System is a very large and complex system software, supports large number of functions. It should be developed as a collection of several smaller modules with carefully defined inputs, outputs and functions rather than a single piece of software. Lets we examine different operating system structure. Layered Structure Approach The operating system architecture based on layered approach consists of number of layers (levels), each built on top of lower layers. The bottom layer is the hardware; the highest layer is the user interface.

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Layer 0 shown Hardware. Layer 1 handled allocation of jobs to processor. Layer 2 implements memory management. The memory management scheme was virtual memory. Layer 3 contained the device driver for the operator's console. Layer 4 contained 1/0 buffering which is above memory management. Layer 5 is user programs which interacts user with operating system. The main advantage of the layered approach is modularity which helps in debugging and verification of the system easily. The layers are designed in such a way that it uses operation and services only if a layer below it. A higher layer need not know how these operations are implemented, only what operations do. Therefore each layer hides implementation details from higher level layers. Any layer can be debugged without any concern about the rest of the layer.  Virtual Machine: It is a concept which creates an illusion of a real machine. It is created by a virtual machine operating system that makes a single real machine appear to be several real machines. This type of situation is analogous to communication line of telephone company which enables separate and isolated conversations over the same write(s). From the user's view point, virtual machine can be made to appear to very similar to existing real machine or they can be entirely different. An important aspect of this technique is that each user can run operating system of his own choice. The virtual machine has many uses and advantages:

1. Concurrent running of dissimilar operating systems by different users.
2. Elimination of certain conversion problem.
3. Software development- programs can be developed and debugged for machine configurations that is different from those of host (for example virtual operating

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Computer Server Systems: It provides an interface to which clients can send requests to perform an action in response to which they execute the action and send back results to the client. File Server Systems: It provides a file system interface where clients can create, update, read and delete files. Advantages of Client-Server Architecture: Organizations often seek opportunities to maintain services and quality competition to sustain its market position with the help of technologies. Deployment of client-server computing in an organization will effectively increase its productivity through the usage of cost-effective user interface, enhanced data storage, vast connectivity and reliable application services.

1. Improved Data Sharing: Data is retained by usual business processes and manipulated on a server is available for designated users (clients) over an authorized access. 2. Integration of Services: Every client is given the opportunity to access corporate information via desktop interface eliminating the necessity to log into a terminal mode or processor. 3. Shared Resources Amongst Different Platforms: Application used for client- server model is built regardless of the hardware platform or technical background of the entitled software (operating system software) providing an open computing environment, enforcing users to obtain the services of clients and servers (database, application and communication services) 4. Data Processing Capability Despite the Location: Client-server users can directly log into a system despite of the location or technology of the processors. 5. Easy Maintenance: Client-server architecture is distributed model representing dispersed responsibilities among independent computers Integrated across a network. Therefore, it's easy to replace, repair, upgrade and relocate a server while client remains unaffected. This unaware change is called as Encapsulation. 6. Security: Servers have better control access and resources to ensure that only authorized clients can access or manipulate data and server updates are administered effectively.

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Disadvantages of Client-Server Architecture:

1. Overloaded Servers: When there are frequent simultaneous client requests, server severely get overloaded, forming traffic congestion. 2. Impact of Centralized Architecture: Since it is centralized, if a critical server failed, client requests are not accomplished. Therefore, client-server lacks the robustness of a good network.  Introduction to basic terms & batch processing system:

1. Jobs
2. Processes files
3. command interpreter. 1. What do you mean by Jobs in Operating System? In certain computer operating systems, a job is the unit of work that a computer operator (or a program called a job scheduler) gives to the operating system. For example, a job could be the running of an application program such as a weekly payroll program. A job is usually said to be run in batch (rather than interactive) mode. The operator or job scheduler gives the operating system a "batch" of jobs to do (payroll, cost analysis, employee file updating, and so forth) and these are performed in the background when time-sensitive interactive work is not being done. 2. What do you mean by processes in Operating System? A process is basically a program in execution. The execution of a process must progress in a sequential fashion. OR A process is defined as an entity which represents the basic unit of work to be implemented in the system. To put it in simple terms, we write our computer programs in a text file and when we execute this program, it becomes a process which performs all the tasks mentioned in the program. When a program is loaded into the memory and it becomes a process. 3. What do you mean by processes file? A batch job is a computer program or set of programs processed in batch mode. This means that a sequence of commands to be executed by the operating system is listed in a file (often called a batch file, command file, job