DMA Controller

DMA
DMA Read Operation:
1. DMAC transfers the data from the I/O device into the main memory.
2. DMAC issues an interrupt to the CPU signaling the reception of data.
3. CPU accesses the main memory and processes the received data

DMA Write Operation:
1. CPU writes the data into the main memory.
2. CPU signals the DMAC to start the transaction.
3. DMAC transfers the data from the main memory into the I/O device.

Two important properties of memory systems
Coherence and Consistency

Coherence concerns only one memory location
Consistency concerns apparent ordering for all locations

Coherence defines the behavior of reads and writes to the same memory location.
Consistency defines the behavior of reads and writes with respect to accesses to other memory locations.