A schematic diagram of the three data transmission models is shown below: PIO First introduce the Programmed I/O (PIO) PIO was widely used in the early days of the PC. Since the speed of the external processor was far greater than that of any other peripheral, the PIO was sufficient for all tasks. For example, if a certain PCI device needs to write some data into memory (SDRAM), the PCI device will request an interrupt from the CPU, and then the CPU first reads the PCI device data into the CPU through the PCI bus. The register is then written from the internal register to the memory (SDRAM). It now appears that the efficiency of this transmission method is still very low. First of all, every CPU and PCI device and SDRAM communication need extra clock cycles (relative to DMA); secondly, this transmission method also needs to occupy the CPU for a long time, which affects the CPU usage rate. Imagine that you are watching a 1080p60 high-definition video online using a PC. This requires Ethernet to continuously write data to the memory (SDRAM). If you use the PIO method, it will be difficult to guarantee the data writing speed. With the current speed of PCI peripherals becoming higher and higher, PIO has been gradually replaced by DMA transmission methods, but in order to be compatible with some early devices, PCI Spec still retains PIO. DMA DMA, Direct Memory Access DMA is a data transmission method that requires almost no CPU intervention during transmission. As the picture above shows, Ethernet can write data directly to memory (SDRAM) with little CPU intervention. In fact, DMA is not only used in the PCI bus system, it is a more widely used method of data transmission. Currently, almost all CPUs and even MCUs support DMA. Specific here is not described in detail, interested can refer to Baidu Encyclopedia: https://baike.baidu.com/item/DMA/2385376?fr=aladdin or other information. Peer-to-Peer In the previous article, we introduced that the identity of the host in the PCI bus system is not fixed but can be switched (by means of an arbiter), but only one host can exist at the same time. The prerequisite for completing the Peer-to-Peer transmission is that there is at least one device capable of becoming a host in the PCI bus system. Under the control of the arbiter, the host identity is switched, and then the PCI bus is controlled, and then communicates with other PCI devices on the bus. However, it should be noted that in the actual system, the Peer-to-Peer transmission method is seldom used because the PCI device (Initiator) acquiring the host identity and another PCI device (Target) are usually used. Different data formats unless they are the same manufacturer's equipment. Pond Fountain Pumps,Fountain Pump,Pond Water Pumps,Electric Fountain Pump Sensen Group Co., Ltd.  , https://www.sunsunglobal.com