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

Resource Allocation Graph in Operating System

Resource Allocation Graph in OS

We use the resource allocation graph for the pictographic representation of the state of a system. The resource allocation graph contains all the information related to the processes that are holding some resources and also waiting for some more resources.

Resource allocation graph consists of all the information which is related to all the instances of the resources means the information about available resources and the resources which the process is being using.

In the Resource Allocation Graph, we use a circle to represent the process and rectangle to represent the resource.

Components of RAG (Resource Allocation Graph)

There are two components of the resource allocation graph:

  1. Vertices
  2. Edges
  1. Vertices: - In the resource allocation graph, we use two kinds of vertices:
Resource Allocation Graph
  • Process Vertices
  • Resource Vertices

Process Vertices: - To represent a process, we use process vertices. We draw the process vertices by using a circle, and inside the circle, we mention the name of the process.

Resource Vertices: - To represent a resource, we use resource vertices. We draw the resource vertices by using a rectangle, and we use dots inside the circle to mention the number of instances of that resource.

According to the number of instances that may exist in the system, there are two types of resource vertices, i.e., single instance and multiple instances.

 Single instance resource type: - In single instance resource type, we use only a single dot inside the box. The single dot indicates that there is one instance of the resource.

Multiple instance resource type: - In multiple instance resource type, we use multiple dots inside the box. Multiple dots indicate that there are various instances of the resources.

2. Edges: - There are two types of edges we use in the resource allocation graph:

Resource Allocation Graph
  • Assign Edges
  • Request Edges

Assign Edges: - We use an assign edge to represent the allocation of resources to the process. We draw assign edges with the help of arrow in which the arrow head points the process, and the process tail points the instance of the resource.

Request Edges: - We use request edge to signify the waiting state of the process. Just like in assign edge, an arrow is used to draw arrow edge. Here, the arrow head points the instance of a resource, and tail of the process points to the process. For example, if a process needs ‘n’ instances of resource type, then we will draw ‘n’ assign edges.

Example of (RAG) Resource Allocation Graph

Example of Single Instance Resource Type

In the following example, we have two processes P1, and P2 and two resources which are R1, and R2. This example is a kind of single instance resource type, and it contain a cycle, so there is a deadlock in the system.

Resource Allocation Graph
          Allocation        Request
       R1     R2      R1     R2
Process P1       1       0        0       1
Process P2       0       1        1       0

                              Available = [R1 R2] = [0 0]

We can see in the following table, there is no instance of resource available, and to execute the process we need a resource. So, no process will be executed, and both the processes keep waiting for a long time. So, we can say that there is a deadlock in the system.

  1. Example of Multiple Instance Resource Type

The term multiple instances means the resources are having more instances. In the following example, we have three processes, which are P1, P2, and, P3 and three resources, which are R1, and R2.                 

Resource Allocation Graph
       Allocation        Request
      R1     R2       R1    R2
 Process P1      1     0        0      1
 Process P2       0     1        1      0
 Process P3       0      1        0       0

Now we check the current Availability = [R1 R2] = [0 0]

Now by using this availability, we check whether we can fulfill the request of any of the processes or not.

We can fulfill the demand or request of P3 because P3 is demanding nothing. So, when the process P3 gets successfully executed, we terminate the process P3.

Then we calculate availability,

             Availability = [0 0] + [0 1]

                                 = [ 0 1]

Now, based on the current availability, we can fulfill the requirement of the P1 process. So, we assign the requested resource to the process P1. When the process P1 executes successfully, then we terminate the process P1.

Now we again calculate availability

           Availablity = [0 1] [1 0]

                              = [1 1]

Now, again based on the current availability we fulfill the requirement of process P2 because the P2 process satisfies the requirement. So, we allocate the requested resource to the Process P2. When the process P2 executes successfully, then it terminates, and we again calculate the availability.

           Availability = [1 1] + [0 1]

                               = [1 2]

So, in this example, there is a safe sequence P3, P1, P2, and all the processes are executed successfully. So, we can say that system is in a safe state, and there is no deadlock in the system.