IDE data transfer mode (PIO, DMA)

With the development of technology, the product has increased the data transmission speed requirement, and the data transmission mode of the IDE interface hard disk has experienced three different technical changes, from the initial PIO mode to the DMA mode to the Ultra DMA mode. . PIO mode The English spelling of PIO is “Programming Input/Output Model”. PIO mode is a data exchange mode in which data is read and written by the CPU executing I/O port commands. It is the earliest hard disk data transmission mode. The data transmission rate is low and the CPU occupation rate is also high. When a large amount of data is transmitted, the system will be suspended due to excessive CPU resources and other operations cannot be performed. PIO data transmission mode is divided into PIO mode 0, PIO mode 1, PIO mode 2, PIO mode 3, PIO mode 4 several modes, data transmission rate from 3.3MB /s to 16.6MB /s. Limited by the low transmission rate and extremely high CPU occupancy, this data transmission mode is quickly eliminated.

DMA Mode The English spelling of DMA is "Direct Memory Access". Chinese means direct memory access. It is a data exchange mode that accesses data directly from memory without going through the CPU. In PIO mode, the data transfer between the hard disk and the memory is controlled by the CPU; in the DMA mode, the CPU only has to issue an instruction to the DMA controller to let the DMA controller handle the number transfer, and then the data transfer is completed. Feedback to the CPU, which greatly reduces the CPU resource occupancy. The difference between the DMA mode and the PIO mode is that the DMA mode does not overly rely on the CPU, which can greatly save system resources, and the difference in transmission speed between the two is not very obvious. The DMA mode can be divided into Single-Word
DMA (single-byte DMA) and Multi- DMA (multi-byte DMA), where the maximum transfer rate can be achieved. It is also only 16.6MB/s.

Ultra DMA Mode Ultra DMA is spelled in English as "Ultra Direct Memory Access", generally abbreviated as UDMA, meaning advanced direct memory access. UDMA mode is based on 16-bit Multi-Word DMA (16-bit multi-byte DMA) mode. It can be understood as an enhanced version of DMA mode. It adds CRC (Cyclic Redundancy) based on the advantages of DMA mode. Check cyclic redundancy code verification technology to improve the accuracy of data transmission and ensure security. In the previous hard disk data transmission mode, only one data is transmitted in one clock cycle, and the Double Data Rate technology is gradually applied in the UDMA mode, so the data transmission speed is greatly improved. This technique is to perform a data transmission during the rising and falling phases of the clock, which can be a multiple of the data transmission speed. After the development of UDMA mode to UDMA133, the technical specifications of the IDE interface are limited, and the connectors, connection cables, and signal protocols all show great technical bottlenecks, and the maximum data transmission rate supported by them is limited. At the same time, the transmission rate of the IDE interface is improved, that is, the working frequency is improved, and the IDE picks up the cat flutter. The defects such as the interference of the living fork, the increase of the ground line, and the signal confusion also bring great constraints to its development, and are replaced by a new generation of SATA. Interface replacement is inevitable.