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Summary of Section 11.1 - The Hardware-Software Interface (C191: Operating Systems for Programmers | zyBooks)

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1. The I/O Hierarchy

A general-purpose computer system includes I/O devices for interaction, storage, and networking. Devices are connected via device controllers, which are electronic circuits operating specific I/O devices using binary signals. These controllers interact with the device driver, a software component implementing I/O operations requested by applications or the OS.

• Device controllers have hardware registers and flags accessible by drivers.
• Device drivers enable OS interaction with devices, abstracting differences in speed, latency, and data format.
• Generic API instructions allow integration of new devices without OS modification. Common categories:
  • Block-oriented devices (e.g., disks, CDs, flash storage)
  • Character-oriented devices (e.g., keyboards, printers, cameras)
  • Network devices (e.g., modems, Ethernet adapters)

Example: A disk driver processes read/write requests, translating high-level instructions into device-specific operations.

2. Programmed I/O with Polling

I/O operations are managed via hardware registers:

• Opcode Register: Specifies requested operation (read/write).
• Operand Registers: Holds operation parameters.
• Busy Flag: Indicates if the device is in use.
• Status Register: Reports success or failure.
• Data Buffer: Stores data for transfer.

With programmed I/O, the CPU manually transfers data between the I/O device and main memory. Polling involves repeatedly checking the busy flag to determine when an operation completes.

Steps in Programmed I/O with Polling

1. The CPU writes an opcode to the device controller.
2. It repeatedly reads the busy flag until the operation is complete.
3. If successful, the CPU copies data from the buffer to memory.