Problems 1 And 2: Computer With Four Processors

For Problems 1 And 2 A Computer Has The Following Four Processes That

For problems 1 and 2, a computer has the following four processes that have arrived in the ready queue in the sequence shown below. NOTE: There are no mandatory time outs required. Process 1 has a run time of 30 seconds, a priority of 1, and it will require 15 seconds of I/O after 10 seconds of execution. Process 2 has a run time of 20 seconds, a priority of 2, and it will require 10 seconds of I/O after 5 seconds of execution. Process 3 has a run time of 25 seconds and a priority of 2. Process 4 has a run time of 10 seconds and a priority of 1. (HINT for problems 1 and 2: Review Module 6 section 2.1.2 for the definitions of these scheduling algorithms and Self-Assessment problems 1-4.)

1. If the Round Robin Scheduling algorithm is used, which process completes second and why?

2. If the Non-preemptive Priority Scheduling algorithm is used, which process completes first? At what time does it complete?

3. Explain the trade-offs between contiguous, noncontiguous linked, and noncontiguous indexed file allocation. In particular, note the effect on sequential and random access methods.

4. Using a variable-partitioned multiprogramming memory, which of the four holes shown below will be used to satisfy a 55 KB program requirement under the conditions of: 0-10 KB 10-55 KB 55-140 KB KB KB KB KB KB KB occupied Hole A occupied Hole B occupied Hole C occupied Hole D occupied ___ First-fit ___ Best-fit ___ Worst-fit (HINT: See Module 6 section 2.2.3 and Self Assessment problem 6.)

Paper For Above instruction

The following analysis explores the scheduling algorithms and memory allocation methods as described in the given problems. By examining the process characteristics and the memory hole sizes, we can determine process completion sequences and suitable memory fit strategies.

Question 1: Round Robin Scheduling - Which process completes second and why?

Round Robin (RR) scheduling assigns each process a fixed time quantum, cycling through processes in a fair manner. Given the process parameters and the processes' arrival order, we can analyze their execution. Assuming a typical time quantum of 10 seconds, the processes are scheduled in a cyclical fashion.

Process 1 (30s, priority 1, I/O after 10s), Process 2 (20s, priority 2, I/O after 5s), Process 3 (25s, priority 2), Process 4 (10s, priority 1). In RR, processes are scheduled in the order they arrive, but since priority is not considered, the sequence is based solely on arrival order.

After the first cycle of 10 seconds, Process 1 and Process 2 have each used some CPU time, with Process 1 needing 20 more seconds and Process 2 needing 10 more seconds. Process 4, requiring only 10 seconds, completes during its first turn. Then, the scheduler continues cycling through the remaining processes.

Process 4 completes after its initial quantum, which is the second process to do so, because it requires only 10 seconds and is scheduled early. The second process to complete is Process 2, which requires 20 seconds, but due to the cycle pattern and the I/O interruptions, Process 2's completion will be delayed relative to other processes with shorter remaining times. Ultimately, Process 2 will complete after Process 3, depending on the exact scheduling order and I/O delays. Since the question asks specifically which process completes second, and considering the typical RR behavior and the process parameters, the second process to complete is Process 2 because its remaining time after initial cycles is longer, but it is scheduled early, and the total process durations imply that Process 4 completes first, then Process 2.

Question 2: Non-preemptive Priority Scheduling - Which process completes first and at what time?

In non-preemptive priority scheduling, the CPU is allocated to the process with the highest priority (lowest priority number) that is ready to execute, and it runs to completion unless it requests I/O.

Given the priorities: Process 1 and Process 4 have priority 1; Process 2 and Process 3 have priority 2. Since Process 1 and Process 4 share the highest priority, the tie-breaker depends on arrival order; assuming Process 1 arrived first, it will execute first.

Process 1, with a run time of 30 seconds, starts immediately, and it is not preempted. It will require 15 seconds of I/O after 10 seconds of execution, which halts its process until I/O completes.

Therefore, the first process to complete is Process 1, but the total time for its completion depends on when its I/O completes. It starts at time 0, runs for 10 seconds, then requires I/O. After completing I/O, which takes 15 seconds, it resumes for the remaining 15 seconds.

Adding these up: 10 seconds + 15 seconds of I/O + 15 seconds of remaining processing = 40 seconds. Therefore, Process 1 completes at 40 seconds under the non-preemptive priority scheduling method.

Question 3: Trade-offs Between File Allocation Methods

In computer systems, file allocation strategies impact both sequential and random access efficiency, as well as storage utilization.

Contiguous Allocation

This method allocates contiguous blocks of disk space for each file, which simplifies sequential access and allows for fast read/write speeds, as data is stored in sequential sectors. However, it suffers from fragmentation—both internal and external—and can lead to inefficient space usage and difficulty in allocating space for larger files as the disk fills up (Tanenbaum & Bos, 2015). This fragmentation complicates dynamic memory management and resizing.

Linked Allocation

In a linked list allocation scheme, each block contains a pointer to the next block, which alleviates external fragmentation. Sequential access is efficient because blocks are linked logically, but random access becomes slow because traversing the list to reach a specific block involves numerous read operations. This scheme is advantageous for sequential reads but less suited to applications requiring frequent random access (Silberschatz, Galvin, & Gagne, 2018).

Indexed Allocation

This method uses an index block containing addresses of all the blocks of a file. It supports both sequential and random access efficiently because the index provides direct access to any block. However, the overhead of maintaining index blocks and their size limitations must be managed. Indexed allocation reduces fragmentation and improves access speed for random access but at the cost of additional disk space for index tables (Stallings, 2014).

In conclusion, each method offers trade-offs: contiguous allocation provides fast sequential access but suffers from fragmentation; linked allocation simplifies dynamic disk space use but hampers random access; indexed allocation balances both, offering good random access performance with some overhead.

Question 4: Memory Allocation in Variable-Partitioned Memory - Hole Selection

Given the memory holes of sizes 0-10 KB, 10-55 KB, 55-140 KB, and occupied regions, determining the appropriate hole depends on the fit strategy:

First-Fit Strategy

First-fit allocates the first hole large enough to accommodate the 55 KB requirement. Starting from the beginning, the first hole of 0-10 KB is too small. The next hole of 10-55 KB is exactly 45 KB, which is insufficient, so skipped. The third hole of 55-140 KB is suitable, as it is 85 KB large. Therefore, under first-fit, the program will be allocated in the 55-140 KB hole.

Best-Fit Strategy

This strategy chooses the smallest hole that fits the requirement. Among the available holes, the 55-140 KB hole is the closest fit, making it the best choice.

Worst-Fit Strategy

Worst-fit assigns the process to the largest available hole to leave larger holes unfragmented. Here, the largest available hole is 55-140 KB, so it will be allocated there as well.

Thus, in all three strategies, the 55-140 KB hole is selected to satisfy the 55 KB requirement.

References

• Tanenbaum, A. S., & Bos, H. (2015). Structured Computer Organization (6th ed.). Pearson.
• Silberschatz, A., Galvin, P. B., & Gagne, G. (2018). Operating System Concepts (10th ed.). Wiley.
• Stallings, W. (2014). Operating Systems: Internals and Design Principles (8th ed.). Pearson.