External Device external device 3 1 Human readable

External Device • ���� external device ������ 3 ����� 1. Human readable ���� video display ��� printer 2. Machine readable ���� magnetic disk ��� sensors 3. Communication ��������

External Device

Typical I/O Data Rates

I/O modules

I/O modules - Function • Control and timing – �������������������� • Processor communication – ���������� I/O module ��� disk �������� READ SECTOR, WRITE SECTOR • Device communication – ����������

I/O modules - Function • Data buffering – ���������� I/O module • Error detection – �������������������� paper jam, bad disk track

Input Output Techniques • ��������� I/O operations 3 ���� – Programmed I/O – Interrupt-driven I/O – Direct Memory Access (DMA)

Programmed I/O

Programmed I/O Memory module 1 CPU 2 READ Check status 3 I/O module peripheral Data

Interrupt-driven I/O

Interrupt-driven I/O Memory module CPU READ Check status I/O module Next Instruction peripheral Data

DMA module

Direct Memory Access Memory module READ CPU Next Instruction DMA module I/O module peripheral Data

����� • William Stalling, Computer Organization and Architecture, USA