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Input/Output

Input/Output. TOPICS Principles of I/O hardware Principles of I/O software I/O software layers Disks Clocks. Chapter 3. Reference: Operating Systems Design and Implementation (Second Edition) by Andrew S. Tanenbaum, Albert S. Woodhull.

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Input/Output

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  1. Input/Output TOPICS Principles of I/O hardware Principles of I/O software I/O software layers Disks Clocks Chapter 3 Reference: Operating Systems Design and Implementation (Second Edition) by Andrew S. Tanenbaum, Albert S. Woodhull

  2. Device Controllers • I/O devices have components: • mechanical component • electronic component • The electronic component is the device controller • may be able to handle multiple devices • Controller's tasks • convert serial bit stream to block of bytes • perform error correction as necessary • make available to main memory

  3. Memory-Mapped I/O (1) Separate I/O and memory space Hybrid Memory-mapped I/O

  4. Memory-Mapped I/O (2) (a) A single-bus architecture (b) A dual-bus memory architecture

  5. Direct Memory Access (DMA) Operation of a DMA transfer

  6. Interrupt How interrupts happens. Connections between devices and interrupt controller actually use interrupt lines on the bus rather than dedicated wires

  7. Principles of I/O Software • Device independence • programs can access any I/O device • without specifying device in advance • (floppy, hard drive, or CD-ROM) • Buffering • data coming off a device cannot be stored in final destination • Error handling • handle as close to the hardware as possible

  8. Programmed I/O (1) Steps in printing a string

  9. Programmed I/O (2) Writing a string to the printer using programmed I/O

  10. Interrupt-Driven I/O • Code executed when print system call is made • Interrupt service procedure

  11. I/O Using DMA • Code executed when print system call is made • Interrupt service procedure

  12. I/O Software Layers Layers of the I/O Software System

  13. Device Drivers • Logical position of device drivers is shown here • Communications between drivers and device controllers goes over the bus

  14. Device-Independent I/O Software (1) Functions of the device-independent I/O software

  15. Device-Independent I/O Software (2) (a) Unbuffered input (b) Buffering in user space (c) Buffering in the kernel followed by copying to user space (d) Double buffering in the kernel

  16. User-Space I/O Software Layers of the I/O system and the main functions of each layer

  17. Disk Formatting • No interleaving • Single interleaving • Double interleaving

  18. Disk Arm Scheduling Algorithms (1) • Time required to read or write a disk block determined by 3 factors • Seek time • Rotational delay • Actual transfer time • Seek time dominates • Error checking is done by controllers

  19. Disk Arm Scheduling Algorithms (2) Pending requests Initial position Shortest Seek First (SSF) disk scheduling algorithm

  20. Disk Arm Scheduling Algorithms (3) The elevator algorithm for scheduling disk requests

  21. Error Handling • A disk track with a bad sector • Substituting a spare for the bad sector • Shifting all the sectors to bypass the bad one

  22. Display Hardware Memory-mapped displays • driver writes directly into display's video RAM Parallel port

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