Operating System Tutorial

Operating System Tutorial Types of Operating System Evolution of Operating System Functions of Operating System Operating System Properties Operating System Services Components of Operating System Needs of the Operating System

Operating Systems

Linux Operating System Unix Operating System Ubuntu Operating System Chrome Operating Systems Fedora Operating System MAC Operating System MS Windows Operating System Solaris Operating System Cooperative Operating System CorelDRAW Operating System CentOS FreeBSD Operating Systems Batch Operating System MS-DOS Operating System Commercial Mobile Operating Systems


Difference Between Multi-programming and Multitasking Difference between C-LOOK and C-SCAN Difference between Rotational Latency and Disk Assess Time Trap vs Interrupt Difference between C-SCAN and SSTF Difference between SCAN and FCFS Difference between Seek Time and Disk Access Time Difference between SSTF and LOOK Difference between Process and Program in the Operating System Difference between Protection and Security in Operating System

How To

How to implement Monitors using Semaphores How to Install a Different Operating System on a PC


What is Kernel and Types of Kernel What is DOS Operating System What is Thread and Types of Thread What is Process Scheduler and Process Queue What is Context Switching What is CPU Scheduling What is Producer-Consumer Problem What is Semaphore in Operating System Monitors in Operating System What is Deadlock What is Paging and Segmentation What is Demand Paging What is Virtual Memory What is a Long term Scheduler What is Page Replacement in Operating System What is BSR Mode What is Convoy Effect What is Job Sequencing in Operating System Why is it critical for the Scheduler to distinguish between I/O-bound and CPU-bound programs Why is there a Need for an Operating System


Process Management Process State Scheduling Algorithm FCFS (First-come-First-Serve) Scheduling SJF (Shortest Job First) Scheduling Round-Robin CPU Scheduling Priority Based Scheduling HRRN (Highest Response Ratio Next) Scheduling Process Synchronization Lock Variable Mechanism TSL Mechanism Turn Variable Mechanism Interested Variable Mechanism Deadlock Avoidance Strategies for Handling Deadlock Deadlock Prevention Deadlock Detection and Recovery Resource Allocation Graph Banker’s Algorithm in Operating System Fixed Partitioning and Dynamic Partitioning Partitioning Algorithms Disk Scheduling Algorithms FCFS and SSTF Disk Scheduling Algorithm SCAN and C-SCAN Disk Scheduling Algorithm Look and C-Look Disk Scheduling Algorithm File in Operating System File Access Methods in Operating System File Allocation Method Directory Structure in Operating System N-Step-SCAN Disk Scheduling Feedback Queue in Operating System Contiguous Memory Allocation in Operating System Real-time Operating System Starvation in Operating System Thrashing in Operating System 5 Goals of Operating System Advantages of Operating System Advantages of UNIX Operating System Bit Vector in Operating System Booting Process in Operating System Can a Computer Run Without the Operating System Dining Philosophers Problem in Operating System Free Space Management in Operating System Inter Process Communication in Operating System Swapping in Operating System Memory Management in Operating System Multiprogramming Operating System Multitasking Operating Systems Multi-user Operating Systems Non-Contiguous Memory Allocation in Operating System Page Table in Operating System Process Scheduling in Operating System Segmentation in Operating System Simple Structure in Operating System Single-User Operating System Two Phase Locking Protocol Advantages and Disadvantages of Operating System Arithmetic operations in binary number system Assemblers in the operating system Bakery Algorithm in Operating System Benefits of Ubuntu Operating System CPU Scheduling Criteria in Operating System Critical Section in Operating System Device Management in Operating System Linux Scheduler in Operating System Long Term Scheduler in Operating System Mutex in Operating System Operating System Failure Peterson's Solution in Operating System Privileged and Non-Privileged Instructions in Operating System Swapping in Operating System Types of Operating System Zombie and Orphan Process in Operating System 62-bit operating system Advantages and Disadvantages of Batch Operating System Boot Block and Bad Block in Operating System Contiguous and Non - Contiguous Memory Allocation in Operating System Control and Distribution Systems in Operations Management Control Program in Operating System Convergent Technologies in Operating System Convoy Effect in Operating System Copy Operating Systems to SSD Core Components of Operating System Core of UNIX Operating System Correct Value to return to the Operating System Corrupted Operating System Cos is Smart Card Operating System Cosmos Operating Systems Examples Generation of Operating System Hardware Solution in Operating System Process Control Block in Operating System Function of Kernel in Operating System Operating System Layers History of Debian Operating Systems Branches and Architecture of Debian Operating Systems Features and Packages of Debian Operating Systems Installation of Operating System on a New PC Organizational Structure and Development in Debian Operating Systems User Interface in Operating System Types Of Memory in OS Operating System in Nokia Multilevel Paging in OS Memory Mapping Techniques in OS Memory Layout of a Process in Operating System Hardware Protection in Operating System Functions of File Management in Operating System Core of Linux Operating System Cache Replacement Policy in Operating System Cache Line and Cache Size in Operating System What is Memory Mapping? Difference Between Network Operating System And Distributed Operating System What is the difference between a Hard link and a Soft Link? Principles of Preemptive Scheduling Process Scheduling Algorithms What is NOS? What is the Interrupt I/O Process? What is Time Sharing OS What is process termination? What is Time-Sharing Operating System What is Batch File File system manipulation What is Message-passing Technique in OS Logical Clock in Distributed System

Privileged and Non-Privileged Instructions in Operating System


It is highly likely that a novice programmer will occasionally execute sensitive code, which could cause the operating system to malfunction and fail. Therefore, we must be able to distinguish between operating system code execution and user system code execution in order to guarantee the operating system's proper operation. The operating system has Dual mode for this purpose. Let's take a quick look at dual-mode in OS before proceeding to the privileged and non-privileged instructions.

Dual Mode in OS

Dual mode is a concept in operating systems that involves the use of two distinct modes of operation or privilege levels: user mode and kernel mode.

  1. User mode is a mode of operation where the operating system restricts the access of running programs to system resources such as memory, processor, and I/O devices. In user mode, programs can only access resources in a controlled and limited way. This is done to prevent user programs from accidentally or intentionally damaging the system or other running programs. User mode is also known as unprivileged mode.
  2. Kernel mode, on the other hand, is a mode of operation where the operating system has full control and unrestricted access to system resources. This mode is used to execute privileged instructions and to manage system resources, such as memory allocation and I/O operations. Kernel mode is also known as privileged mode.

The dual-mode concept is used to ensure the safety and security of the operating system and the programs running on it. By running in user mode, programs are prevented from interfering with the operating system or other running programs, and by running in kernel mode, the operating system can manage system resources and perform privileged operations. When a program needs to perform a privileged operation or access a system resource that is restricted in user mode, it must request the operating system to switch to kernel mode temporarily to execute the operation. This is done through a system call, which is a mechanism provided by the operating system to allow user programs to request privileged services.

Life Cycle of Instruction

The life cycle of an instruction in an operating system can be broken down into four main stages: fetch, decode, execute, and store. These stages are performed in both user mode and kernel mode, depending on the type of instruction being executed.

  1. Fetch: The first stage is fetching the instruction from memory. The processor reads the instruction from memory and stores it in a special register called the instruction register (IR). The location of the instruction is determined by the program counter (PC), which holds the memory address of the next instruction to be executed.
  2. Decode: In this stage, the processor decodes the instruction in the IR to determine what operation needs to be performed. This involves interpreting the opcode and any operands that are included in the instruction.
  3. Execute: The execute stage is where the operation specified by the instruction is performed. This can involve performing arithmetic or logical operations on data stored in memory or registers, or it can involve accessing I/O devices or interacting with the operating system through system calls.
  4. Store: The final stage is storing the result of the operation back to memory or registers. This allows subsequent instructions to access the result of the operation.

When a user application is started, the control is switched to user mode, and instructions are executed in this mode. However, when a system call, interrupt, or trap occurs, the control is switched to kernel mode to allow the operating system to perform privileged operations, such as accessing hardware or modifying system settings. Once the privileged operation is complete, control is returned to the instruction following the system call, and instructions continue to be executed in user mode. This process of switching between user mode and kernel mode during the execution of instructions allows for the safe and efficient operation of the operating system.

Types of instructions

 An instruction is a command or order that an application gives to the system. There are two types of instructions in the operating system: privileged instructions and non-privileged instructions. Prior to that, we'll talk about privileged instructions.

What are Privileged Instructions?

The instructions that can only be executed in kernel mode are referred to as privileged instructions.

A privileged instruction will be ignored and treated as an illegal instruction if it is attempted to be executed in user mode. The hardware keeps it in the operating system.

Before transferring control to any user application, the operating system is responsible for ensuring that the Timer is set to interrupt. Consequently, in the event that the timer is interrupted, the operating system can regain control.

To guarantee proper operation, the operating system makes use of privileged instruction.

  1. I/O instructions
  2. Context switching
  3. Clear memory
  4. Set the CPU's timer
  5. Halt instructions
  6. Interrupt management
  7. Modify entries in the Device-status table

What are Non-Privileged Instructions?

Instructions that are only carried out in user mode are referred to as non-privileged instructions.

Examples of non-privileged instructions include the trap instruction, reading system time, reading processor status, sending output to the printer, and performing arithmetic operations. The layered organization of the operating system will now be depicted in the figure.

There are two parts to the computer system as a whole: software and hardware. Using the instruction set, the software and hardware interact with one another.

There are two types of the instruction set:

Special instructions: Because of the potential for misuse, these instructions must be followed with care.

Non-advantaged guidelines: These are standard directions.

Based on the instructions, there are two categories for the software component:

  1. Kernel: only able to carry out privileged instructions.
  2. Application: can carry out instructions, both privileged and non-privileged.
Privileged and Non-Privileged Instructions

Differences between Privileged and Non-Privileged instructions in an Operating System:

FeaturePrivileged InstructionsNon-Privileged Instructions
ExecutionCan only be executed in kernel or supervisor modeCan be executed in user mode
AccessHave access to all system resources, including hardwareLimited access to system resources, with some restrictions
PurposeUsed to perform privileged operations, such as memory management and I/O control.Used to perform basic operations, such as arithmetic and logical operations.
SecurityCan potentially compromise system security if executed incorrectly or maliciouslyGenerally pose a lower security risk than privileged instructions
ExamplesInterrupt and trap handling instructions, memory management instructions, I/O instructionsArithmetic instructions, logical instructions, data transfer instructions, control instructions