Operating Systems I/O Module
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Questions and Answers

What is the average seek time of the disk in milliseconds?

  • 6
  • 2
  • 4 (correct)
  • 8

    • How many sectors are there in each track?

  • 700
  • 600
  • 400
  • 500 (correct)

    • What is the total time to read a file consisting of 2500 sectors using sequential organization in milliseconds?

  • 100
  • 64 (correct)
  • 40
  • 80

    • What is the rotational delay in milliseconds?

    <p>4</p> Signup and view all the answers

    Why do the next tracks not need seek time in sequential organization?

    <p>Due to contiguous storage</p> Signup and view all the answers

    What is the total time to read a file consisting of 2500 sectors using random access in milliseconds?

    <p>20,040</p> Signup and view all the answers

    What is the main reason for differences in performance among disk scheduling policies?

    <p>Seek time</p> Signup and view all the answers

    What is the initial location of the disk head?

    <p>Track 100</p> Signup and view all the answers

    What is the primary benefit of integrating DMA and I/O functions?

    <p>It substantially cuts the required bus cycles.</p> Signup and view all the answers

    What is the main advantage of using an I/O bus to connect I/O modules to the DMA module?

    <p>It reduces the number of I/O interfaces in the DMA module.</p> Signup and view all the answers

    Why is efficiency a major concern in I/O design?

    <p>I/O devices are relatively slow compared to main memory.</p> Signup and view all the answers

    What is the primary goal of using multiprogramming in I/O operations?

    <p>To allow one process to execute while another waits on I/O.</p> Signup and view all the answers

    What is the main benefit of using a hierarchical modular design of I/O functions?

    <p>It hides the details of device I/O in lower-level routines.</p> Signup and view all the answers

    What is the primary disadvantage of using swapping in I/O operations?

    <p>It is an I/O operation itself.</p> Signup and view all the answers

    What is the main goal of I/O design in terms of efficiency?

    <p>To improve the efficiency of disk I/O.</p> Signup and view all the answers

    What is the main benefit of using a uniform manner of handling I/O devices?

    <p>It allows processes to see devices in general terms.</p> Signup and view all the answers

    What does the CPU do with the I/O processor?

    <p>Directs the I/O processor to execute an I/O program in main memory</p> Signup and view all the answers

    What is a characteristic of an I/O module?

    <p>It has its own local memory and is used to control communications with interactive terminals</p> Signup and view all the answers

    What does the DMA module send to the processor when the data transfer is complete?

    <p>An interrupt signal</p> Signup and view all the answers

    What is the function of the DMA module in a data transfer operation?

    <p>To transfer data directly to or from memory, over a bus, without going through the CPU</p> Signup and view all the answers

    What is a disadvantage of the Single Bus DMA configuration?

    <p>It is inefficient due to processor-controlled programmed I/O</p> Signup and view all the answers

    What is the primary purpose of I/O buffering?

    <p>To overlap I/O with processing and increase efficiency</p> Signup and view all the answers

    How does the CPU delegate the I/O operation to the DMA module?

    <p>By sending R/W requests, using R/W control lines, to the DMA module</p> Signup and view all the answers

    What happens if a process is swapped out while waiting for I/O to complete?

    <p>A deadlock can occur</p> Signup and view all the answers

    What information is sent to the DMA module via data lines?

    <p>All of the above</p> Signup and view all the answers

    What is the main difference between block-oriented and stream-oriented buffering?

    <p>The way data is stored and transferred</p> Signup and view all the answers

    What happens to the CPU while the DMA module is transferring data?

    <p>It continues with other work</p> Signup and view all the answers

    Which type of buffering is typically used for disks and USB keys?

    <p>Block-oriented buffering</p> Signup and view all the answers

    What is the main advantage of using I/O buffering?

    <p>.allowing processes to overlap I/O with processing</p> Signup and view all the answers

    What happens to the pages involved in an I/O transfer if buffering is not used?

    <p>They are locked in memory</p> Signup and view all the answers

    What type of devices typically use stream-oriented buffering?

    <p>Terminals, printers, and communication ports</p> Signup and view all the answers

    What is the main problem that can occur if a process is swapped out during I/O operations?

    <p>Deadlock</p> Signup and view all the answers

    Which disk scheduling algorithm selects the disk I/O request that requires the least movement of the disk arm from its current position?

    <p>Shortest Service Time First (SSTF)</p> Signup and view all the answers

    What is the limitation of the Shortest Service Time First (SSTF) algorithm?

    <p>It does not guarantee that the average seek time over a number of arm movements will be minimum</p> Signup and view all the answers

    Which disk scheduling algorithm is also known as the Elevator or LOOK policy?

    <p>SCAN</p> Signup and view all the answers

    Which disk scheduling algorithm favors jobs whose requests are for tracks nearest to both the innermost and outermost tracks?

    <p>SCAN</p> Signup and view all the answers

    What is the main difference between SCAN and C-SCAN algorithms?

    <p>SCAN moves in both directions, while C-SCAN moves in one direction only</p> Signup and view all the answers

    What is the benefit of using C-SCAN over SCAN?

    <p>C-SCAN reduces the maximum delay experienced by new requests</p> Signup and view all the answers

    Which disk scheduling algorithm is better than FIFO in terms of performance?

    <p>SSTF</p> Signup and view all the answers

    Which disk scheduling algorithm avoids starvation of new requests?

    <p>SCAN</p> Signup and view all the answers

    Study Notes

    I/O Module and DMA

    • An I/O module is a separate processor that executes an I/O program in main memory, directed by the CPU.
    • The I/O module has its own local memory and is commonly used to control communications with interactive terminals.

    Direct Memory Access (DMA)

    • The CPU delegates I/O operations to the DMA module, which transfers data directly to or from memory without going through the CPU.
    • The DMA module sends an interrupt signal to the processor when the transfer is complete.
    • DMA configurations can be single bus, integrated DMA and I/O, or I/O bus.

    DMA Configurations

    • Single Bus: all modules share the same system bus, with the DMA module acting as a surrogate processor.
    • Integrated DMA and I/O: integrates DMA and I/O functions, reducing bus cycles.
    • I/O Bus: connects I/O modules to the DMA module, reducing the number of I/O interfaces in the DMA module.

    Operating System Design Issues

    • Efficiency: I/O devices are slow compared to main memory, and I/O cannot keep up with processor speed.
    • Generality: it is desirable to handle all I/O devices in a uniform manner, using a hierarchical modular design of I/O functions.

    I/O Buffering

    • Performs input transfers in advance and output transfers some time after the request is made.
    • Reasons for buffering: overlap I/O with processing, increase efficiency, and avoid interference with swapping decisions.

    Types of I/O Devices

    • Block-oriented Buffering: information is stored in fixed-sized blocks, used for disks and USB keys.
    • Stream-Oriented Buffering: transfers information as a stream of bytes, used for terminals, printers, and communication ports.

    Timing Comparison

    • Calculating the total time for a file transfer: consider seek time, rotational delay, and transfer time.

    Disk Scheduling Policies

    • Importances of reducing average seek time to improve performance.
    • Policies include:

    Shortest Service Time First (SSTF)

    • Selects the disk I/O request that requires the least movement of the disk arm from its current position.

    SCAN

    • Arm moves in one direction only, satisfying all outstanding requests until it reaches the last track in that direction.
    • Also known as Elevator or LOOK policy.

    C-SCAN

    • Restricts scanning to one direction only, reducing the maximum delay experienced by new requests.

    Comparison of Disk Scheduling Algorithms

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    Description

    This quiz covers the concept of I/O modules in operating systems, including their functionality and interaction with the CPU and main memory.

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