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Important Short Questions and Answers: Processes and Operating Systems

Embedded Systems- Important Short Questions and Answers: Processes and Operating Systems



1. Define Process.


Process can be defined as a program unit in execution the state of which is controlled by OS. It is a single execution of a program. Process is also defined as computational unit, which is scheduled and runs on the CPU by a kernel. Kernel controls the creation of the process and states of the process.


2. Define Thread.


Thread is a light weight process. Processes that share the same address space are often called threads.



3. What are multi rate systems?


Multirate embedded computing systems are very common, including automobile engines, printers, and cell phones. In all these systems, certain operations must be executed periodically, and each operation is executed at its own rate.


4. What is release time and deadline of a process?


The release time is the time at which the process becomes ready to execute. A deadline specifies when a computation must be finished. The deadline for an aperiodic process is generally measured from the release time, since that is the only reasonable time reference.


5. What is the period and rate of a process?


The period of a process is the time between successive executions. The process’s rate is the inverse of its period.


6. What is a task graph?

A set of processes with data dependencies is called a task graph.


7. Define CPU utilization.

Utilization is the ratio of the CPU time that is being used for useful computations to the

total available CPU time. This ratio ranges between 0 and 1, with 1 meaning that all of the

available CPU time is being used for system purposes.


8. What are the three basic scheduling states of a process?

Waiting state


Ready state and

Execution state.


9. Define scheduling policy.


A scheduling policy defines how processes are selected for promotion from the ready state to the running state.


10. What is hyperperiod?


Hyperperiod is the least-common multiple of the periods of all the processes. It is a finite period that covers all possible combinations of process executions.


11. What is scheduling overhead?


The execution time required to choose the next execution process, which is incurred in addition to any context switching overhead is the scheduling overhead.


12. What do you mean by a context switch?


The set of registers that define a process are known as its context and switching from one process’s register set to another is known as context switching.


13. What is process control block?

The data structure that holds the state of the process is known as the process control




14. What are two major ways to assign priorities to a process?


There are two major ways to assign priorities: static priorities that do not change during execution and dynamic priorities that do change.


15. What is Rate monotonic analysis (RMS)?


The Rate monotonic analysis is the theory behind the Rate monotonic scheduling. The simple model of the system is as follows,


All processes run periodically on a single CPU. Context switching time is ignored.


There are no data dependencies between processes. The execution time for a process is constant.


All deadlines are at the ends of their periods.


The highest-priority ready process is always selected for execution.


16.            What is the response time and critical instant of a process?

The response time of a process is the time at which the process finishes.


The critical instant for a process is defined as the instant during execution at which the task has the largest response time.


17. What are the two ways of process communication?


A process can send a communication in one of two ways: blocking or Non-blocking. After sending a blocking communication, the process goes into the waiting state until it receives a response. Non-blocking communication allows the process to continue execution after sending the communication.


18. Define earliest deadline first scheduling (EDF)?


Earliest deadline first (EDF) is a scheduling policy which uses a dynamic priority scheme—it changes process priorities during execution based on initiation times. As a result, it can achieve higher CPU utilizations than RMS. The EDF policy is very simple: It assigns priorities in order of deadline. The highest-priority process is the one whose deadline is nearest in time, and the lowest priority process is the one whose deadline is farthest away.


19. Define preemption.

Preemption is the act of forcing a process out of execution i.e. making a context switch.


20.            If your set of processes is un-schedulable and you need to guarantee that they complete their deadlines, give possible ways to solve this problem?


The techniques available are as follows Get a faster CPU.


Redesign the processes to take less execution time Rewrite the specification to change the deadlines


21.            What is priority inversion problem?


Priority inversion is a situation where in lower priority tasks will run blocking higher priority tasks waiting for a resource. The two processes may deadlock.



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