Operating System Articles - Page 120 of 179

Let us understand the privileged instructions in an operating system.Privileged instructionsThese are called machine level instructions that are executed when the processor is in privileged mode.The examples include the following −Shut down the systemChange the contents of a control register.Jump into kernel code.Sending commands to I/O devices.The processor is said to be in privileged mode when the functions in the OS kernel are executing.Suppose an attempt is made to execute a privileged instruction in non-privileged mode which causes a run-time error.Generally the user mode of the operating system is called non-privileged mode and kernel mode of the operating system is ... Read More

The five process states in the Linux kernel are as follows −Running − This is a state where a process is either in running or ready to run. It is the most active state of all. In this state, the process is getting system resources.Interruptible − This state is a blocked state of a process which waits for an event or a particular time slot.Uninterruptible − It is also a blocked state and it has a timeout value before going to sleep. It will awake when the timeout value sets off.Stopped − Once the process is completed, this state occurs ... Read More

Let us begin by understanding the types of process states.Types of Process StatesThere are different types of Process States which are as follows −New − The process is about to be created in this state but not yet created, it is the program which is present in secondary memory that will be picked up by OS to create the process.Ready − The process enters the ready state after the creation of a process that means the process is loaded into the main memory.Running − The process is chosen by the CPU for instructions and the executions within the process and ... Read More

Let us understand what a process state is.Process StatesProcess states are the states in which the process is currently residing. There are basically five states of processes −New − The process is about to be created in this state but not yet created. It is the program which is present in secondary memory that will be picked up by OS to create the process.Ready − The process enters the ready state after the creation of a process that means the process is loaded into the main memory.Running − The process is chosen by the CPU for instructions and the executions ... Read More

Threads that are available at user level are called as user threads. Threads available at kernel level are called kernel threads. User threads are supported above the kernel and are managed without kernel support and kernel threads are supported and managed directly by the operating system.Types of multithreading modelsThe different types of multithreading models are as follows −Many-to-one modelIt maps many user threads to one kernel thread. The thread management is based on the thread library in user space, because of this it is efficient but the entire process is going to block if a thread makes a blocking system ... Read More

Process scheduler assigns different processes to CPU based on particular scheduling algorithms.The scheduling is responsible for taking part in the scheduling process that is the set of the policies and mechanisms to control the order in which the jobs can be completed. By using the scheduling algorithms the scheduler is done.Types of Process Scheduling AlgorithmsThe different types of process scheduling algorithms are as follows −FCFS(First Come First Serve)SJF or shortest job next.Round Robin.Shortest Remaining time.Priority Scheduling.Multiple level queues.The scheduling criterion is responsible for helping in the design of the good scheduler. These criteria are as follows −CPU UtilizationThe scheduling algorithm ... Read More

Before working on the difference between all three schedulers, let us recall the concept of process scheduler.Process scheduler is a part of the Operating system which schedules the process. If the process is in ready, waiting and running state it schedules it correctly and is also responsible for the allocation of the CPU processor to a specific task within a time interval.Also, when the task or process is completed it doesn't allow the CPU to sit idle. It will allocate the other task depending on its current state. If the process was in ready state it will allocate it to ... Read More

The processes that are entering into the system are stored in the Job Queue. Suppose if the processes are in the Ready state are generally placed in the Ready Queue.The processes waiting for a device are placed in Device Queues. There are unique device queues which are available for every I/O device.First place a new process in the Ready queue and then it waits in the ready queue till it is selected for execution.Once the process is assigned to the CPU and is executing, any one of the following events occur −The process issue an I/O request, and then placed ... Read More

A thread is a small unit of CPU utilisation. It comprises a thread ID, a program counter, a register set and a stack. It shares with other threads which belong to the same process having code segment, data section and other operating system resources like open files and signals.A heavy weight process has a single thread of control. If a process has multiple threads of control, it can perform more than one task at a time. Many software packages that run in modern PC’s are multi-threaded. Here, the application is implemented as a separate process with several threads of control.For ... Read More

Micro kernel is one of the classifications of kernel and is often represented as μ- kernel. It is software which provides a mechanism to implement an operating system.The functions or mechanism for implementation are as follows −Inter-process communicationThread managementLow level address space managementIn the micro kernel, user services and kernel services are kept in different address spaces. User services are placed in user address space. Kernel services are placed in kernel services. Therefore, the size of the kernel and size of the operating system is minimized or reduced.Given below is the diagram of micro kernel −It is very secure and ... Read More