Operating Systems tutorials

General Definition of Operating Systems An OS is a program which acts as an interface between computer system users and the computer hardware. It provides Read More »

Operating System History It all started with computer hardware in about 1945s. Computers were using vacuum tube technology. Programs were loaded into memory manually using switches, Read More »

Overview: A process is an executing program, including the current values of the program counter, registers, and variables.The subtle difference between a process and a Read More »

Process States Overview: we have already read the concept of process ,not let us see what it is process states, please check the below figure Read More »

What is Scheduler in Operating System ? If we consider batch systems, there will often be more processes submitted than the number of processes that can Read More »

In order to achieve an efficient processor management, OS tries to select the most appropriate process from the ready queue. For selection, the relative importance of Read More »

Now, let’s discuss some processor scheduling algorithms again stating that the goal is to select the most appropriate process in the ready queue. For the Read More »

In a multi-programming system, in order to share the processor, a number of processes must be kept in memory. Memory management is achieved through memory management algorithms. Read More »

Why Paging is Required ? Paging permits a program to allocate noncontiguous blocks of memory. The OS divide programs into pages which are blocks of small Read More »

Every access to memory should go through the page table. Therefore, it must be implemented in an efficient way. a. Using fast dedicated registers Keep page Read More »

Concept Of Segmentation in Operating System In segmentation, programs are divided into variable size segments, instead of fixed size pages. Every logical address is formed of Read More »

Lets Discuss Virtual Memory Over here ,All the memory management policies we have discussed so far, try to keep a number of processes in the memory Read More »

If there is no page fault, effective access time is effective memory acces time is eatNO-PF = emat If there is a page fault, we Read More »

Why Dirty Bit? What is Dirty Bit? In order to reduce the page fault service time, a special bit called the dirty bit can be associated Read More »

A page replacement algorithm determines how the victim page (the page to be replaced) is selected when a page fault occurs. The aim is to minimize Read More »

Deadlocks Definition: In a multiprogramming system, processes request resources. If those resources are being used by other processes then the process enters a waiting state. However, Read More »

Resource allocation graphs are drawn in order to see the allocation relations of processes and resources easily. In these graphs, processes are represented by circles Read More »

Deadlock Prevention:To prevent the system from deadlocks, one of the four discussed conditions that may create a deadlock should be discarded. The methods for those conditions Read More »

Given some additional information on how each process will request resources, it is possible to construct an algorithm that will avoid deadlock states. The algorithm will Read More »

Banker’s Algorithm (Dijkstra and Habermann):It is a deadlock avoidance algorithm. The following data structures are used in the algorithm: m = number of resources n Read More »

If a system has no deadlock prevention and no deadlock avoidance scheme, then it needs a deadlock detection scheme with recovery from deadlock capability. For this, Read More »

If the system is in a deadlock state, some methods for recovering it from the deadlock state must be applied. There are various ways for recovery: Read More »

Processes frequently need to communicate with other processes. For example, in a shell pipeline, the output of the first process must be passed to the second Read More »

The problem of avoiding race conditions can also be formulated in an abstract way. Part of the time, a process is busy doing internal computations Read More »

Disabling Interrupts The simplest solution is to have each process disable all interrupts just after entering its CS  and re-enable them just before leaving it. Read More »

By combining the idea of taking turns with the idea of lock variables and warning variables, in 1965, a Dutch mathematician, T. Dekker, was the Read More »

E. W. Dijkstra suggested using an integer variable for IPC problems. In his proposal, a new variable type, called a semaphore, was introduced. Dijkstra proposed having Read More »

Besides its usage for CS problem, semaphores can also be used for synchronization of the processes. For example consider two concurrent processes: p1, p2. We require Read More »

Assume there are n slots capable of holding one item. Process producer will produce items to fill slots and process consumer will consume the items in Read More »

Imagine a big database, such as an airline reservation system, with many competing processes wishing to read and write. It is acceptable to have multiple processes Read More »

There are N philosophers spending their lives thinking and eating in a room. In their round table there is a plate of infinite rice and N Read More »

The barber shop has one barber, one barber chair, and N chairs for waiting customers, if any, to sit in. If there is no customer at Read More »