Interface type
Parallel interface mainly as a printer port, using a 25-pin D couple. The so-called "parallel" means that the 8-bit data is transmitted simultaneously through a parallel line, so that the data transfer speed is greatly improved, but the length of the line transmitted in parallel is limited, because the length increases, the interference will increase, and the data is easier to errors. The computer is basically equipped with parallel port. Serial port port is called a serial interface, and the PC typically has two serial ports COM 1 and COM 2. The serial port is different from the parallel port in that its data and control information are transmitted in one position. Although this speed will be slow, the transfer distance is longer than in parallel, so the serial port should be used when the long distance is communicated. Usually, COM 1 uses 9-pin D-shaped connector, also known as the RS-232 interface, and some of COM 2 uses an old-fashioned DB25 pin connector, also known as RS-422 interface, but already rarely use. Typical case
Typical case
USB, "Universal Serial Bus", Chinese name is a universal serial bus. This is a new interface technology that is gradually applied in the PC field in recent years. The USB interface has the characteristics of faster transfer speed, hot swap and connecting multiple devices. It has been widely used in various external equipment. There are two USB interfaces: USB1.1 and USB2.0. Theoretically, the transmission speed of USB1.1 can reach 12Mbps / second, and USB 2.0 can reach the speed of 480MB / sec, and can be compatible with USB1.1. Usually most people are used to connect other mobile devices such as mobile phones or U disks.