Input output hardware of operating system

operating System

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

2. Overview
What is I/O?
Categories of I/O Devices
Device drivers & Device controllers
Communication in I/O devices
Polling & Interrupts
Input & Output 2CSE-2018

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
Input & Output 3CSE-2018

4. Categories
Block Devices
Character Devices
Input & Output 4CSE-2018

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
Input & Output 7CSE-2018

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