Skip to main content

What is a system call in operating systems?

CPU executes a program either in USER MODE or KERNEL MODE.

Most of the Kernel Mode processes will be, basic level core functionalities of system and such processes will have direct accesess to most of the available resources of the system.

Most of the User Mode processes will be of third party programs, which may be hazardes to a computet if we give direct access to resources.

So for a program running in user mode must have to uses Operating System APIs inorders to access resources with out any security breaches.

For such accesess the process in User Mode have to call OS functions with APIs provided, is known as system calls.

Comments

Popular posts from this blog

Operating Systems | Scheduling Algorithms : Round Robin

| FCFS | SJF | SRTS | Round Robin | LJF | Priority Scheduling | HRRN | Round RobinFeatures : Most popular algorithm of allPractically implementableImplementable with basic data structures like queueExtremely lesser starvationOptimum efficiency can be set by controlling time quantumThe round robin algorithm will continuously switch between processes if a process in CPU (under execution) exceeds a time limit set by OS called time quantum.Flow Chart :Scheduler allocated process to for execution.CPU starts monitoring the execution time right after from allocation.If the process completes its execution before exceeding time quantum, OS forwards the process to termination state.else, the processes gets preempted once the time quantum limit exceeded and if the process finished at this moment, OS moves the process to termination state, else it moves to ready queue and iterates over the whole process listed above.Example : Consider the following table of processes and calculate complet…

Operating Systems | Concept of Process

Hard disk drive of the system in called primary memory and secondary memory is Random Access Memory(RAM). Either a program written in High Level Language(HLL) or a executable code generated by the sequence of works done by pre-processor, compiler and assembler, resides in secondary memory of the system. To start an execution, operating system allocates some space in the main memory, for the program to be executed and loads the program in the secondary memory to the allocated space. The piece of work which is loaded by the operating system to the main memory in order to execute program is called processEvery program loaded by operating system will create a focus boundary(or process body), a partitioned memory area where all memory requirements for the execution of program is satisfied.Variable which will not change its value through out life time of process is called static variable and variables which are globally accessible in a process known as global variable.Heap area is reserved f…

Operating Systems | Scheduling Algorithms : SJF

| FCFS | SJF | SRTS | Round Robin | LJF | Priority Scheduling | HRRN | Shortest Job First(SJF)SJF algorithm schedules the shortest job(low burst time) available on main memory at the time of context switching in ready state . It can be either preemptive or non-preemptive depending on the nature of scheduler.Since the SJF select the job which is shorted among available jobs on main memory, Non-preemptive SJF algorithm will have larger waiting time if a job with longer burst time get scheduled first. In short SJF is also vulnerable to Convoy EffectTo find shortest process among min-heap would be the best data structure to be usedExample : Consider the following table of processes and calculate completion time, turn around time and waiting time using SJF algorithm with the following assumptions. No preemption.No I/O request will be there from any process.Arrival time is relative to CPU on time.Process NumberATBT103222324442View Answer

The execution of processes can be visualized …