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Without DMA, when the CPU is using programmed input/output, it is often fully occupied for the entire duration of the learn or write operation, and is thus unavailable to perform other work. With DMA, the CPU first initiates the switch, then it does different operations whereas the switch is in progress, and it finally receives an interrupt from the DMA controller (DMAC) when the operation is finished. This feature is useful at any time that the CPU can't keep up with the speed of information switch, or when the CPU needs to perform work whereas waiting for a relatively sluggish I/O data switch. Many hardware methods use DMA, including disk drive controllers, graphics playing cards, community cards and sound playing cards. DMA can be used for intra-chip information switch in some multi-core processors. Computer systems that have DMA channels can switch information to and from gadgets with a lot much less CPU overhead than computers with out DMA channels. Equally, a processing circuitry inside a multi-core processor can transfer data to and from its native memory with out occupying its processor time, permitting computation and knowledge transfer to proceed in parallel.

DMA can also be used for "memory to memory" copying or transferring of information within memory. DMA can offload expensive memory operations, resembling large copies or scatter-gather operations, from the CPU to a dedicated DMA engine. An implementation instance is the I/O Acceleration Technology. DMA is of curiosity in network-on-chip and in-memory computing architectures. Customary DMA, additionally referred to as third-social gathering DMA, makes use of a DMA controller. A DMA controller can generate Memory Wave addresses and provoke Memory Wave Protocol read or write cycles. It incorporates several hardware registers that can be written and skim by the CPU. These embody a memory handle register, a byte depend register, and one or more control registers. Relying on what options the DMA controller gives, these management registers would possibly specify some mixture of the source, the destination, the route of the transfer (studying from the I/O gadget or writing to the I/O gadget), the scale of the switch unit, and/or the number of bytes to switch in a single burst.

To carry out an enter, output or memory-to-memory operation, the host processor initializes the DMA controller with a depend of the number of words to transfer, and the memory tackle to make use of. The CPU then commands the peripheral machine to initiate a data switch. The DMA controller then gives addresses and skim/write management strains to the system memory. Every time a byte of knowledge is able to be transferred between the peripheral device and memory, the DMA controller increments its internal address register till the total block of data is transferred. Some examples of buses utilizing third-celebration DMA are PATA, USB (before USB4), and SATA; nonetheless, their host controllers use bus mastering. In a bus mastering system, often known as a primary-party DMA system, the CPU and peripherals can each be granted management of the Memory Wave bus. Where a peripheral can become a bus grasp, it could actually directly write to system memory without the involvement of the CPU, offering memory handle and control alerts as required.

Some measures must be provided to place the processor into a hold situation in order that bus contention does not occur. In burst mode, a whole block of knowledge is transferred in a single contiguous sequence. As soon as the DMA controller is granted entry to the system bus by the CPU, it transfers all bytes of knowledge in the information block earlier than releasing management of the system buses again to the CPU, but renders the CPU inactive for comparatively lengthy durations of time. The mode can be called "Block Switch Mode". The cycle stealing mode is used in methods through which the CPU should not be disabled for the length of time wanted for burst switch modes. Within the cycle stealing mode, the DMA controller obtains entry to the system bus the identical way as in burst mode, using BR (Bus Request) and BG (Bus Grant) alerts, that are the two signals controlling the interface between the CPU and the DMA controller. Nonetheless, in cycle stealing mode, after one unit of data transfer, the control of the system bus is deasserted to the CPU via BG.