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With out DMA, when the CPU is using programmed input/output, it is usually absolutely occupied for MemoryWave the complete 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 other operations while the switch is in progress, and it lastly receives an interrupt from the DMA controller (DMAC) when the operation is completed. This characteristic is beneficial at any time that the CPU can not keep up with the rate of data transfer, or when the CPU needs to carry out work whereas waiting for a relatively gradual I/O knowledge transfer. Many hardware techniques use DMA, including disk drive controllers, graphics cards, network cards and sound playing cards. DMA is also used for intra-chip data transfer in some multi-core processors. Computer systems that have DMA channels can switch data to and from gadgets with much much less CPU overhead than computers without DMA channels. Similarly, a processing circuitry inside a multi-core processor can transfer knowledge to and from its local memory without occupying its processor time, permitting computation and knowledge transfer to proceed in parallel.

DMA can be used for "memory to memory" copying or moving of knowledge inside memory. DMA can offload costly memory operations, reminiscent of massive 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. Commonplace DMA, additionally known as third-occasion DMA, uses a DMA controller. A DMA controller can generate memory addresses and provoke memory learn or write cycles. It incorporates a number of hardware registers that may be written and read by the CPU. These embrace a memory address register, a byte count register, and one or more management registers. Relying on what features the DMA controller supplies, these control registers might specify some combination of the source, the vacation spot, MemoryWave the course of the transfer (reading from the I/O gadget or writing to the I/O machine), the dimensions of the switch unit, and/or the number of bytes to switch in one burst.

To carry out an enter, output or memory-to-memory operation, the host processor initializes the DMA controller with a count of the number of words to switch, and the memory handle to make use of. The CPU then commands the peripheral system to provoke an information transfer. The DMA controller then gives addresses and browse/write management lines to the system memory. Each time a byte of data is able to be transferred between the peripheral device and memory, the DMA controller increments its internal tackle register until the total block of information is transferred. Some examples of buses utilizing third-party DMA are PATA, USB (before USB4), and SATA; however, their host controllers use bus mastering. In a bus mastering system, often known as a first-social gathering DMA system, the CPU and peripherals can each be granted management of the memory bus. The place a peripheral can become a bus grasp, it might immediately write to system memory without the involvement of the CPU, providing memory handle and management signals as required.

Some measures have to be offered to place the processor right into a hold condition so that bus contention does not happen. In burst mode, a whole block of knowledge is transferred in one contiguous sequence. Once the DMA controller is granted entry to the system bus by the CPU, it transfers all bytes of data in the info block before releasing management of the system buses again to the CPU, however renders the CPU inactive for comparatively lengthy intervals of time. The mode can be called "Block Switch Mode". The cycle stealing mode is utilized in programs wherein 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 same manner as in burst mode, using BR (Bus Request) and BG (Bus Grant) alerts, which are the two indicators controlling the interface between the CPU and the DMA controller. Nevertheless, in cycle stealing mode, after one unit of data switch, the control of the system bus is deasserted to the CPU by way of BG.