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
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