Operating Systems Questions

Scheduling is the activity of the deciding when process will receive the resources they request.

FCS ---> FCSFS stands for First Come First Served. In FCFS the job that has been waiting the longest is served next.

Round Robin Scheduling--->Round Robin scheduling is a scheduling method where each process gets a small quantity of time to run and then it is preempted and the next process gets to run. This is called time-sharing and gives the effect of all the processes running at the same time

Shortest Job First ---> The Shortest job First scheduling algorithm is a nonpreemptive scheduling algorithm that chooses the job that will execute the shortest amount of time.

Priority Scheduling--->Priority scheduling is a scheduling method where at all times the highest priority process is assigned the resource.

Selects from among the processes in memory that are ready to execute, and allocates the CPU to one of them. CPU scheduling decisions may take place when a process: 1.Switches from running to waiting state. 2.Switches from running to ready state. 3.Switches from waiting to ready. 4.Terminates. Scheduling under 1 and 4 is non-preemptive. All other scheduling is preemptive.

Waiting state

• Program execution


• I/O operations


• File system manipulation


• Communication


• Error detection


• Resource allocation


• Accounting


• Protection

In Windows NT, executive refers to the operating system code that runs in kernel mode.

DRAM is not the best, but it’s cheap, does the job, and is available almost everywhere you look. DRAM data resides in a cell made of a capacitor and a transistor. The capacitor tends to lose data unless it’s recharged every couple of milliseconds, and this recharging tends to slow down the performance of DRAM compared to speedier RAM types.

It is a technique proposed by Lamport, used to order events in a distributed system without the use of clocks. This scheme is intended to order events consisting of the transmission of messages. Each system 'i' in the network maintains a counter Ci. Every time a system transmits a message, it increments its counter by 1 and attaches the time-stamp Ti to the message. When a message is received, the receiving system 'j' sets its counter Cj to 1 more than the maximum of its current value and the incoming time-stamp Ti. At each site, the ordering of messages is determined by the following rules: For messages x from site i and y from site j, x precedes y if one of the following conditions holds....(a) if Ti

• Job queue


• Ready queue


• Device queue