Computer I/O Systems Quiz
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Questions and Answers

What is an advantage of memory-mapped I/O?

  • Simplifies data transfer with multiple buses
  • Requires special instructions for reading control registers
  • Does not require separate control signals (correct)
  • Provides direct access to I/O devices in user space

    • In programmed I/O (PIO), what must the program do before reading input from a device?

  • Request permission from the operating system
  • Enable the device's data bus
  • Test whether the device is ready with the input (correct)
  • Direct the user to input data

    • Which data transfer method requires the program to repeatedly test a status bit before proceeding?

  • Bus Mastering
  • Programmed I/O (PIO) (correct)
  • Direct Memory Access (DMA)
  • Interrupt Driven I/O

    • What is a primary function of Direct Memory Access (DMA)?

    <p>To enable data transfer without CPU intervention</p> Signup and view all the answers

    What are the two main jobs of a computer as outlined in the context?

    <p>I/O and processing</p> Signup and view all the answers

    Which characteristic is NOT typically associated with I/O systems?

    <p>Minimal influence on performance</p> Signup and view all the answers

    What type of I/O devices includes disks and tapes?

    <p>Storage devices</p> Signup and view all the answers

    Which of the following is NOT a component of I/O hardware interfacing?

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

    How does the CPU typically communicate with device registers and data buffers?

    <p>Through memory-mapped I/O or separate I/O ports</p> Signup and view all the answers

    What is a major issue concerning I/O systems in terms of overall system performance?

    <p>Impact on performance and perception</p> Signup and view all the answers

    Which device category is responsible for such components as keyboards and mice?

    <p>Human-interface devices</p> Signup and view all the answers

    What trend is seen with I/O device technology?

    <p>Increasing standardization of software and hardware interfaces</p> Signup and view all the answers

    What is a disadvantage of programmed I/O (PIO)?

    <p>It may result in prolonged wait states.</p> Signup and view all the answers

    How does an interrupt-driven I/O system respond to events?

    <p>It utilizes a signal from devices to process events.</p> Signup and view all the answers

    What is the role of I/O ports in communication between the processor and devices?

    <p>They serve as memory addresses for device communication.</p> Signup and view all the answers

    What happens to the CPU during an interrupt?

    <p>It saves the current instruction pointer and jumps to the interrupt handler.</p> Signup and view all the answers

    Why is Direct Memory Access (DMA) beneficial for large data transfers?

    <p>It allows the CPU to perform other tasks simultaneously.</p> Signup and view all the answers

    Which component of an I/O port indicates whether a byte is available to be read?

    <p>Status register</p> Signup and view all the answers

    What is the primary purpose of the CPU's interrupt-request line?

    <p>To signal the occurrence of an interrupt after each instruction.</p> Signup and view all the answers

    What is a disadvantage of using I/O ports compared to memory-mapped I/O?

    <p>It is less flexible and powerful.</p> Signup and view all the answers

    In memory-mapped I/O, how does the processor treat I/O devices?

    <p>Like any other memory location.</p> Signup and view all the answers

    What type of I/O method does programmed I/O rely on?

    <p>Continuous hardware checking in a loop.</p> Signup and view all the answers

    What is the main issue with using programmed I/O for devices that generate asynchronous events?

    <p>It may cause the CPU to engage in excessive waiting.</p> Signup and view all the answers

    What must a host do to start a command in an I/O port?

    <p>Write to the control register.</p> Signup and view all the answers

    Which of the following is NOT a function of the status register in an I/O port?

    <p>Storing temporary data.</p> Signup and view all the answers

    What initiates a DMA transfer?

    <p>The host writes a DMA command block into memory.</p> Signup and view all the answers

    Which statement about I/O ports is correct?

    <p>No two devices can share the same I/O port.</p> Signup and view all the answers

    What is one advantage of using I/O ports over memory-mapped I/O?

    <p>The architecture is simpler and less complicated.</p> Signup and view all the answers

    What is the primary role of a DMA controller?

    <p>To facilitate memory transfers without CPU intervention</p> Signup and view all the answers

    Under which condition is using DMA deemed unnecessary?

    <p>When the CPU is faster than the DMA controller</p> Signup and view all the answers

    What is one advantage of buffering data in DMA controllers?

    <p>It allows the bus to handle additional tasks</p> Signup and view all the answers

    What task is typically performed by device drivers?

    <p>Check the validity of input parameters</p> Signup and view all the answers

    Why might placing device drivers in user space be considered beneficial?

    <p>To prevent system crashes due to bad drivers</p> Signup and view all the answers

    Which of the following describes the behavior of drivers in the I/O system?

    <p>Drivers block themselves until the interrupt is processed</p> Signup and view all the answers

    How do interrupt handlers function in an I/O system?

    <p>They wake up the driver when an I/O operation finishes</p> Signup and view all the answers

    What is a potential drawback of using a non-standard driver interface?

    <p>Difficulty in maintaining device compatibility</p> Signup and view all the answers

    What is the primary reason for using a standard interface for driver functions?

    <p>To avoid the complications of creating a new interface for each device type.</p> Signup and view all the answers

    How does the OS map symbolic device names to drivers in Unix?

    <p>It maps them to an i-node containing major and minor device numbers.</p> Signup and view all the answers

    Which buffering method allows a process to handle multiple incoming characters efficiently?

    <p>Double buffering in the kernel</p> Signup and view all the answers

    What is a common protection mechanism used to prevent unauthorized access to I/O devices?

    <p>Implementing a file protection system</p> Signup and view all the answers

    What happens during unbuffered input when a process reads data from a modem?

    <p>Each character arrival interrupts the process awaiting the next character.</p> Signup and view all the answers

    Which of the following is NOT a function of independent software in relation to I/O devices?

    <p>Allocating devices that can be shared among multiple users.</p> Signup and view all the answers

    Which scenario highlights a challenge faced when using buffering in user space?

    <p>Potential data loss if the buffer is paged out while new data arrives.</p> Signup and view all the answers

    Which of the following accurately describes the role of user space I/O software?

    <p>It includes library routines that facilitate user interaction with I/O.</p> Signup and view all the answers

    Study Notes

    I/O Systems Overview

    • I/O is a significant part of computer operation, alongside processing.
    • It's the most complex subsystem within an operating system (OS).
    • OS engineers frequently work on I/O because of the high rate of code change.
    • Testing I/O is challenging and critical for system performance and acceptance.

    I/O Devices

    • I/O devices vary greatly in type and characteristics, requiring diverse interfacing within the OS.
    • Two key trends in I/O device technology are increasing standardization and a growing variety of I/O devices.
    • These devices include block and character devices.
    • Devices are categorized by hardware such as ports, buses, and controllers.
    • I/O devices also have software components such as device drivers.

    Modern I/O Systems

    • Modern I/O systems feature various components including, graphics controllers, bridge/memory controllers, disk controllers, IDE disk controllers, SCSC controllers, keyboard, and more.
    • These components are connected through various bus systems like PCI, expansion buses, parallel, and serial ports.

    I/O Hardware Categories

    • Storage devices (disks, tapes)
    • Transmission devices (network cards, modems)
    • Human-interface devices (screen, keyboard, mouse)
    • Specialized devices (e.g. game controllers)

    I/O Hardware Data Rates (example table)

    • Devices like keyboards have low data rates (10 bytes/sec). -In contrast, fast Ethernet has a high data rate of 12.5 MB/sec.

    I/O Devices: Hardware Interfacing

    • Interfacing mediums include wired and wireless connections.
    • Interfacing components within I/O systems encompass ports (e.g., serial port) and buses (connection for multiple devices).
    • Device controllers manage device communication.

    CPU Communication with Control Registers and Device Data Buffers

    • I/O controllers have registers for OS reading and writing.
    • OS uses registers for commands and status checks.
    • Device data buffers store input/output data.
    • There are various ways to direct CPU data transfer through registers and buffers (separate I/O ports, memory-mapped I/O, and hybrid approaches).

    I/O Ports

    • I/O ports are memory addresses used for direct processor communication with devices.
    • A hexadecimal number, specific to each device, is assigned as a port address.
    • Devices share I/O ports (not possible in previous OS systems).
    • Multiple registers (e.g., a status register, command register, Data-in and data-out registers) are involved during I/O communication.

    I/O Ports: Advantages and Disadvantages

    • Advantages: Simplified system architecture; generally faster than other methods.
    • Disadvantages: Requires more instructions compared to other methods; less powerful and flexible.

    Memory-Mapped I/O

    • Processor treats I/O devices like memory locations.
    • I/O devices share memory space with RAM and ROM.
    • Same memory instructions are used for I/O and memory transfers from the CPU.
    • There are single and dual bus architectural approaches
    • Advantages: Simple programming, no unique hardware instructions required.
    • Disadvantages: Shared memory can lead to conflicts during simultaneous access.

    Data Transfer Methods Between CPU and Device

    • Programmed I/O (PIO): CPU directly polls device status and transfers data one byte at a time.
    • Interrupt-driven I/O: Device signals the CPU when ready to transfer data.
    • Direct Memory Access (DMA): DMA controller handles data transfer directly between device and memory to reduce CPU involvement.

    Programmed I/O (PIO)

    Description: CPU repeatedly checks if the device is ready (polling).

    • Input Transfer: CPU reads device status bits and reads data from the device after confirming readiness.
    • Output Transfer: CPU checks if the device's output buffer is ready and writes the data.

    Interrupt-Driven I/O

    • Devices signal the CPU when ready (interrupt).
    • CPU processes the interrupt.
    • Data transfer takes place.

    Direct Memory Access (DMA)

    • DMA controller handles data transfer directly between memory and device.
    • CPU isn't involved in the data transfer process.
    • CPU is only involved at the start of a transfer or when an error occurs.

    I/O Interfacing: Interrupts

    • CPU has an interrupt-request wire.
    • CPU monitors this wire for interrupts from devices.
    • Upon interrupt, the CPU saves context, jumps to handler, processes the reason for the interrupt and returns to the previous context.

    Clock Hardware and Software

    • Clock hardware consists of a crystal oscillator and counter.
    • Clock software handles time of day, process time limits, CPU usage accounting, alarm handling, watchdog timers, and profiling.

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    Related Documents

    I/O Systems PDF

    Description

    Test your knowledge on Input/Output systems in computer architecture. This quiz covers topics such as memory-mapped I/O, programmed I/O, and Direct Memory Access (DMA). Understand the advantages and disadvantages of different I/O methods and device categories.

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