I/O Techniques

I/O Operations is the operation of inserting or extracting data to/from the computer system.

I/O Techniques refers to how I/O operations are executed.

There are 3 ways to perform the I/O operations (I/O Techniques):

• Programmed I/O
• CPU has direct control over I/O
• Sensing Status
• Read/Write Commands
• Transferring data
• CPU need to waits for I/O module to complete Operation.
• It wastes CPU time.
• Interrupt-Driven I/O  
• Overcomes CPU waiting 
• No repeated CPU Checking of device
• I/O module interrupts when ready
• Direct Memory Access (DMA)
• Interrupt driven and programmed IO require active CPU intervention
• transfer rate is limited
• CPU is tied up
• Interrupt driven and programmed I/O require active CPU intervention
• Transfer rate is limited
• CPU is tied up 
• Additional Module (hardware) on bus
• DMA controller takes over from CPU for I/O
• The I/O module and main memory exchange data directly, without CPU involvement

Picture below show how the Programmed I/O works:

Programmed I/O

The picture below show how Interupt Driven I/O:

Interupt Driven I/O

Direct Memory Access is the answer to I/O techniques:

Direct Memory Access