Input Output Techniques:

o   Interrupt driven

o   Direct Memory Access (DMA)

o   Programmed

Programmed I/O

•   CPU has control over I/O directly
•   Read/write commands
•   Sensing status
•   Transferring data
•   Wastes CPU time
•   CPU waits for I/O module to finish operation
•   I/O module performs operation
•   I/O module sets status bits
•   CPU requests I/O operation
•   CPU checks status bits periodically
•   I/O module doesn't inform CPU directly
•   I/O module does not interrupt CPU
•   Under programmed I/O data transfer is similar memory access (CPU viewpoint)
•   Each device given unique identifier
•   CPU may wait or come back later
•   CPU commands have identifier (address)

I/O Mapping

•   Large selection of the memory access commands available
•   Memory mapped I/O

o   memory and Devices share an address space

o   I/O looks like memory read/write

o   No special commands for I/O

•   Restricted set
•   Isolated I/O

o   Separate address spaces

o   Need I/O or memory select lines

o   Special commands for I/O