By the end of this Subject, we will be able to learn:
General Definition An OS is a program which acts as an interface between computer system users and the computer hardware. It provides a user-friendly environment Read More »
It all started with computer hardware in about 1945s. Computers were using vacuum tube technology. Programs were loaded into memory manually using switches, punched cards, or paper Read More »
Definition: 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 program Read More »
we have already read the concept of process ,not let us see what it is process states, please check the below figure States 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 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 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, 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 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 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 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 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 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 »
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