This document discusses input and output hardware and devices. It describes I/O devices as those that send information to computers for processing or reproduce processed results. The document categorizes I/O devices as block devices that communicate in entire blocks of data or character devices that communicate byte by byte. It also discusses device drivers, controllers, synchronous vs asynchronous communication, and techniques for communication like memory mapping, DMA, polling, and interrupts.

1. Input & Output Hardware
Operating Systems
Input & Output 1CSE-2018

2. Overview
 What is I/O?
 Categories of I/O Devices
 Device drivers & Device controllers
 Communication in I/O devices
 Polling & Interrupts
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3. What is I/O Device ?
 An input device sends information to a computer system for
processing, and an output device reproduces or displays the
results of that processing
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4. Categories
 Block Devices
 Character Devices
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5. Block Devices Character Devices
 Driver communicates by
sending entire block of data
 Ex- Harddisk ,Usb
Cameras..etc  Driver communicates by
sending
characters(Bytes,Octets)
 Ex- Serial ports, Parralel
ports
Input & Output 5CSE-2018

6. Device driver Device controllers
 Software modules that
handles a particular device.
 OS needs it to handle all
I/O devices.
 Works as interface b/w
device & device drivers.
 It converts serial bit streams
into block of bytes.
Input & Output 6CSE-2018

7. Synchronous Vs Asynchronous OS
 CPU execution waits while
I/O proceeds.
 I/O proceeds concurrently
with CPU execution
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8. Communication to I/O devices
 Three approaches…
 Special Instruction I/O
 Memory-mapped I/O
 DMA (Direct Memory access)
Input & Output 8CSE-2018

9. Special instruction I/O
CPU instructions , specially made to control I/O devices.
Memory-mapped I/O
The device is connected directly to certain main memory
locations
OS allocates buffer in memory and informs I/O device to use
that buffer to send data to the CPU.
Memory mapped IO is used for most high-speed I/O devices
like disks, communication interfaces.
Input & Output 9CSE-2018

10. Direct Memory Access (DMA)
 DMA means CPU grants I/O module authority to
read from or write to memory without involvement.
 DMA module itself controls exchange of data
between main memory and the I/O device.
Input & Output 10CSE-2018

11. Polling
 Polling is the simplest way for an I/O device to
communicate with the processor.
 The I/O device simply puts the information in a
Status register, and the processor must come and get
the information.
 This is an inefficient method and much of the
processors time is wasted on unnecessary polls.
Input & Output 11CSE-2018

12. Interrupts
 An interrupt is a signal to the microprocessor from a
device that requires attention.
 When the interrupting device has been dealt with,
the CPU continues with its original task as if it had
never been interrupted.
Input & Output 12CSE-2018