Questions and Answers
What is the primary purpose of the status register in a canonical device?
Which of the following is a disadvantage of device polling?
What happens when an interrupt is raised by a device?
Why is a hierarchical structure important in system architecture?
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What is a function of the command register in a canonical device?
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What does the operating system primarily need to know about a device?
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How does an interrupt improve CPU utilization?
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What is the result of the OS issuing a request to a device?
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What is a potential issue with using interrupts in a system?
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What is the hybrid approach suggested for managing device communication?
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What phenomenon occurs when an OS only processes interrupts?
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How can the overhead of Programmed I/O (PIO) be reduced?
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Which statements regarding memory-mapped I/O are correct?
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What is a recommended strategy when the speed of a device is unknown?
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What advantage does coalescing provide in interrupt management?
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What is the function of I/O instructions in device communication?
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Study Notes
I/O Devices Overview
- I/O devices serve as interfaces for input and output in computer systems.
- Integration of I/O in system architecture is essential for efficiency.
Hierarchical Structure Necessity
- Faster buses require a shorter physical design.
- High-performance buses are expensive to engineer.
Modern System Architecture
- Uses Direct Media Interface (DMI) to improve data transfer efficiency.
Canonical Device Components
- Status Register: Indicates the current operational state of the device.
- Command Register: Sends instructions for device operations.
- Data Transfer: Involves passing data to or from the device.
OS Interaction with Devices
- Utilizes hardware interfaces via registers for communication.
- Key requirements for the OS:
- Monitor device status (busy/free).
- Provide specific instructions.
- Transfer data as needed.
Polling Device Mechanism
- Uses programmed I/O (PIO) for device communication.
- Polling can lead to inefficiencies, wasting CPU resources by waiting instead of executing tasks.
Interrupt Mechanism
- OS sends a request and places the calling process into a sleep state, enabling context switching to ready tasks.
- Upon task completion, the device generates a hardware interrupt, prompting the CPU to execute the Interrupt Service Routine (ISR), which resumes the waiting process.
Advantages of Interrupts
- Allows overlapping operations between communication and I/O.
- Enhances overall resource utilization compared to polling.
Interrupt Issues
- Fast devices may lead to inefficiencies due to regular context switching and interrupt handling.
- High-frequency interrupts (e.g., from network packets) can cause livelock, where the OS only handles interrupts.
Solution to Interrupt Issues
- Hybrid Approach: Switch between polling and interrupts based on device speed.
- Coalescing: Merges multiple interrupts into one, reducing the interrupt load.
Data Movement Challenges
- PIO can overload the CPU when transferring large volumes of data.
Direct Memory Access (DMA)
- DMA engines facilitate data transfers between devices and memory with minimal CPU involvement, improving overall system performance.
Communication with Devices
- I/O Instructions: Direct communication to device registers, using privileged in and out instructions on x86 systems.
- Memory-Mapped I/O: Device registers accessed as memory locations, allowing the OS to use load/store instructions for data transfer.
Building a Device-Neutral OS
- The focus is on creating an OS that can effectively manage diverse devices without needing specific communication methods for each.
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Description
This quiz explores the essential functions and architectures of I/O devices in computer systems. It covers topics such as the hierarchical structure of buses, the role of registers in OS interaction, and polling mechanisms for device communication. Test your knowledge on the integration of I/O in modern system designs.
