I/O: Input-Output

1. I/O: Input-Output By: Tommy Zeng

2. What is I/O? • I/O – short for “Input – Output” • How a computer interacts with its users • Input – gets information from the outside world and puts it in the computer • Output – gets information from the computer and puts it out into the world

3. Input Devices • Keyboard • Mouse

4. Output Devices • Monitor • Printer

5. Performing I/O • Two ways to perform input-output • Primitive I/O instructions • Memory-mapped I/O

6. Primitive I/O Instructions • Related to CPU architecture • Hard-coded into the CPU • “input from port #...” • “output to port #...”

7. Memory-mapped I/O • Related to system memory • Input and output devices are “mapped” to certain memory addresses • Read from a mapped address means to read from a specific input device • Write to a mapped address means to output to a specific output device

8. I/O Overlap • CPU cannot execute instructions while waiting for I/O request • CPU goes into a wait state when I/O request is issued • Must go into “I/O overlap”

9. I/O Overlap • I/O transfers controlled by I/O subsystem instead of CPU • Subsystems include Direct Memory Access (DMA) controller

10. DMA Controller • DMA controller handles I/O operations • Allows CPU to execute other instructions while I/O is being performed

11. Recap • Get Input from input devices • Displays output through output devices • Memory-mapping allows more flexible I/O Operations • DMA Controller allows CPU to continue processing while I/O operations are being performed