High School

Consider a swapping system that has a series of holes (all in MB) with the following sizes (in order): 9, 20, 15, 22, 18, 17, 19, 31, 11, 14. Three processes of sizes 9, 11, and 13 MB arrive in order. Select the correct order of the holes selected if a best fit strategy is used.

b) In a demand-paged system, what is a page-fault? Outline the procedure by which a page-fault is handled.

c) Describe the way files are organized in a single-level directory. What are the main two problems of this structure? Describe another directory structure that addresses the problems of the single-level directory.

d) A process that requires 8.2 MB of space is swapped to a hard disk. The transfer rate to the disk is 108.4 MB/s, and there is a further latency of 7.3 microseconds. Calculate the total context switch swapping time (that is, swap out and swap in) of this process. Write down your answer in milliseconds.

Answer :

Final answer:

A best fit strategy for a swapping system would select the holes in the order 9, 17, 18, 19, 20, 22, 31, 15. In a demand-paged system, a page-fault occurs when a requested page is not found in the main memory and needs to be brought in from the hard disk. The two problems of a single-level directory structure are naming conflicts and difficulty in organizing and finding files, which can be addressed by using a multi-level or hierarchical directory structure.

Explanation:

Best Fit Strategy for Swapping System:

  1. 9, 17, 18, 19, 20, 22, 31, 15 - First process of size 9 MB fits into the first hole of size 9 MB exactly.
  2. 9, 17, 18, 19, 20, 22, 31, 15 - Second process of size 11 MB fits into the second hole of size 11 MB exactly.
  3. 9, 17, 18, 19, 20, 22, 31, 15 - Third process of size 13 MB fits into the second hole of size 18 MB after a best fit.

Page Fault in a Demand-Paged System:

A page-fault occurs when a requested page is not found in the main memory (RAM) and needs to be brought in from the secondary storage (hard disk).

The procedure to handle a page-fault typically involves the operating system searching for an available page frame in the main memory, swapping out a page if necessary, and then bringing in the requested page from the hard disk into the newly allocated page frame.

Single-Level Directory Structure:

In a single-level directory structure, files are organized in a flat directory where all files are stored in a single directory.

The two main problems of this structure are naming conflicts when files have the same name, and difficulty in organizing and finding files when there are a large number of files.

Multi-Level or Hierarchical Directory Structure:

A multi-level or hierarchical directory structure addresses the problems of the single-level directory by organizing files into a tree-like structure with directories nested within other directories.

This allows for better organization, avoids naming conflicts by providing unique paths to each file, and makes it easier to locate and access files.

Context Switch Swapping Time Calculation:

Given transfer rate = 108.4 MB/s

Given latency = 7.3 microseconds = 0.0073 milliseconds

Transfer time = (8.2 MB) / (108.4 MB/s) = 0.0756 milliseconds

Total context switch swapping time = Transfer time + Latency = 0.0756 milliseconds + 0.0073 milliseconds = 0.0829 milliseconds

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