Question

I would like Question 3 answered please

i. What is the total elapsed time for the two processes to run to completion? ii. Assume the system runs a non-preemptive scheduler where proceses are scheduled in the order in which they become runnable, and that B takes priority over A in the event of a tie. Give the combined execution pattern of the two processes in the format as in part b), and determine the total elapsed time for the two processes to run to completion. Repeat part b) ii) with a pre-emptive scheduler operating with a time slice of 4 ms. iv. What are the costs and the benefits of a pre-emptive over a non-preemptive scheduler for this workload, which would you choose, and why? Exercise 4 120 points)

Answer 1

1. Interrupt:  In system programming, an interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention.
2. Polled Mode Operation : In computer science, refers to actively sampling the status of an external device by a client program as a synchronous activity. Polling is most often used in terms of input/output (I/O), and is also referred to as polled I/O or software-driven I/O.
3. Direct Memory Access : Direct memory access (DMA) is a feature of computer systems that allows certain hardware subsystems to access main system memory (random-access memory), independent of the central processing unit (CPU).

CPU-I/O Burst Cycle :

• Almost all processes alternate between two states in a continuing cycle, as shown in Figure 6.1 below :
  • A CPU burst of performing calculations, and
  • An I/O burst, waiting for data transfer in or out of the system.

load store add store read from file CPU burst wait for IVO IVO burst store increment index write to file CPU burst wait for IVO I/O burst load store add store read from file CPU burst wait for l/VO I/O burst

Alternating sequence of CPU and I/O bursts

* CPU bursts vary from process to process, and from program to program, but an extensive study shows frequency patterns similar to that shown in Figure

Histogram of CPU-burst durations

CPU bound means the program is bottlenecked by the CPU, or central processing unit, while I/O bound means the program is bottlenecked by I/O, or input/output, such as reading or writing to disk, network, etc. In general, when optimizing computer programs, one tries to seek out the bottleneck and eliminate it.

And

In computer science, I/O bound refers to a condition in which the time it takes to complete a computation is determined principally by the period spent waiting for input/output operations to be completed. This is the opposite of a task being CPU bound.

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