Hardware interrupts:

Hardware interrupts-from I/O devices, processor, memory Software interrupts-produced by a program.

Direct Memory Access (DMA)

 Interrupt or Polling driven I/O incurs considerable overhead

• Saving program state
• Incrementing memory addresses
• Multiple program instructions
• Keeping track of word count

Transfer  high  amounts  of  data  at  high  speed  without  continuous  intervention  by  the processor

DMA controller keeps track of memory locations, directly transfers to memory (using the bus)

independent of the processor

Special control circuit needed in the I/O device interface which is called a DMA controller