1. What is an Operating system?

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An operating system is a program that manages the computer hardware.It also provides a basis for application programs and acts as an intermediary between the computer user and the computer hardware.

2.What are the main objectives of the operating system?

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The main objectives of the operating system are as follows: To make the computer system convenient to use in an efficient manner.

• To hide the details of the hardware resources from the users.
• To provide users a convenient interface to use the computer system.
• To act as an intermediary between the hardware and its users, making it easier for the users to access and use other resources.
• To manage the resources of a computer system.
• To keep track of who is using which resource, granting resource requests, and mediating conflicting requests from different programs and users.
• To provide efficient and fair sharing of resources among users and programs.

3.Explain the various evolution of operating systems.

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The various evolution of an operating system are given below:
i)Serial Processing: was developed from 1940 to 1950’s programmers incorporated the hardware components without the implementation of the operating system.
ii)Batch Processing: is used by improving the utilization and application of computers. Jobs were scheduled and submitted on cards and tapes. Then sequentially executed on the monitors by using Job Control Language.
iii)Multiprogramming Multiprogramming is a technique to execute a number of programs simultaneously by a single processor. In multiprogramming, a number of processes reside in the main memory at a time.
iv)Time-Sharing System: Time-sharing or multitasking is a logical extension of multiprogramming. Multiple jobs are executed by the CPU switching between
v)Parallel System: There is a trend of multiprocessor systems, such systems having more than one processor in close communication, sharing the computer bus, the clock, and sometimes memory and peripheral devices.
vi)Distributed System: In a distributed operating system, the processors cannot share a memory or a clock, each processor has its own local memory.

4.What Is Access Control ?

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Functions of the operating system:
i) Memory Management
ii)Processor Management/Scheduling
iii) Device Management
iv) File Management
v)Security
vi)Accounting
vii)Other functions
i )Memory Management: It is the management of the main or primary memory.
ii)Processor Management/Scheduling: When more than one process runs on the system the OS decides how and when a process will use the CPU. Hence, the name is also CPU Scheduling.
iii)Device Management: Device management in an operating system means controlling the Input/Output devices like disk, microphone, keyboard, printer, magnetic tape, USB ports, camcorder, scanner, other accessories, and supporting units like supporting units control channels.
iv)File Management: A file management system is used for file maintenance (or management) operations.
v)Security: The term operating system (OS) security refers to practices and measures that can ensure the confidentiality, integrity, and availability (CIA) of operating systems.
i)Accounting: The operating system keeps track of all the functions of a computer system. Hence, it makes a record of all the activities taking place on the system.
ii)Other functions: Some other functions of the OS can be:

• Error detection.
• keeping a record of system performance.
• Communication between different software etc.

5.Classify the operating system based on structure.

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)Simple structure: Such operating systems do not have a well-defined structure and are small, simple, and limited systems.
i)Layered structure:The layered structure approach breaks up the operating system into different layers and retains much more control on the system. The bottom layer (layer 0) is the hardware, and the topmost layer (layer N) is the user interface.
ii)Micro-kernel: structure designs the operating system by removing all non-essential components from the kernel and implementing them as system and user programs. This results in a smaller kernel called the micro-kernel.
v)Monolithic Approach: Functionality of the OS is invoked with simple function calls within the kernel, which is one large program.

6. What is Linux Kernel?

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The Linux kernel is the main component of a Linux operating system (OS) and is the core interface between a computer’s hardware and its processes. It communicates between the two, managing resources as efficiently as possible.

7. What are the core subsystems of the Linux kernel?

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The Core Subsystems of the Linux Kernel are as follows:

• The Process Scheduler
• The Memory Management Unit (MMU)
• The Virtual File System (VFS)
• The Networking Unit
• Inter-Process Communication Unit

8. Define System calls.

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A system call is a routine that allows a user application to request actions that require special privileges. Adding system calls is one of several ways to extend the functions provided by the kernel.

9. What are the categories of System calls?

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The followings are the main categories of System calls:
i) Process Control: running program needs to be able to stop execution either normally or abnormally. When execution is stopped abnormally, often a dump of memory is taken and can be examined with a debugger.
ii)File Management: Some common system calls are created, delete, read, write, reposition, or closed. Also, there is a need to determine the file attributes – get and set file attributes. Many times the OS provides an API to make these system calls.
iii)Device Management: Processes usually require several resources to execute, if these resources are available, they will be granted and control returned to the user process.
iv)Information Management: system calls exist purely for transferring information between the user program and the operating system. An example of this is time or date.
v)Communication: are two models of interprocess communication, the message-passing model and the shared memory model.

• Message-passing uses a common mailbox to pass messages between processes.
• Shared memory uses certain system calls to create and gain access to create and gain access to regions of memory owned by other processes. The two processes exchange information by reading and writing in the shared data.

10. What are the system calls used in OS?

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There are the following system calls used in OS:
i)wait()
ii)fork()
iii)exec()
iv)kill()
v)exit()

11. What is the function of fork()?

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Processes use fork() system call to create processes that are a copy of themselves. With the help of this system Call parent process creates a child process, and the execution of the parent process will be suspended till the child process executes.

12. What is kernel?

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The kernel is a core component of an operating system and serves as the main interface between the computer’s physical hardware and the processes running on it. The kernel enables multiple applications to share hardware resources by providing access to CPU, memory, disk I/O, and networking.

13. What are User Mode and Kernel Mode?

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User Mode: In User mode, the executing code has no ability to directly access hardware or reference memory. Code running in user mode must delegate to system APIs to access hardware or memory. Due to the protection afforded by this sort of isolation, crashes in user mode are always recoverable. Most of the code running on our computer will execute in user mode.
Kernel Mode: In Kernel mode, the executing code has complete and unrestricted access to the underlying hardware. It can execute any CPU instruction and reference any memory address. Kernel mode is generally reserved for the lowest-level, most trusted functions of the operating system. Crashes in kernel mode are catastrophic; they will halt the entire PC.