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The data cable is a necessary component to connect the hard disk and the motherboard, and it is usually included when purchasing the motherboard. Each data line can only connect two IDE devices (such as optical drives, hard disks, recorders, etc.) [1] . COM interface
COM interface is also called serial port. Most motherboards in the past provided two COM ports, COM1 and COM2.
The role of the COM interface is to connect devices such as a serial mouse and an external Modem.
The 1/O address of the COM1 interface is 03F8h-03FFh, and the interrupt number is IRQ4;
The 1O address of the COM2 interface is O2F8h-O2Fh, and the interrupt number is IRQ3.
Therefore, the COM2 interface has priority over the response of the COM1 interface. Later, serial devices such as mouse adopted PS2 interface and the current popular USB interface, and external devices based on serial port are rare [6] .
USB interface
The full name of USB is Universal Serial Bus, which means "Universal Serial Bus" in Chinese. USB was jointly proposed by Intel, Compaq, IBM, and other companies at the end of 1994. USB supports hot-plug, and its advantages of plug-and-play make it the most important interface method for computers [3] .
The USB interface has 4 pins, which are the USB power supply (usually 5V), the USB data line +, the USB data line and the ground line [3] .
USB has two specifications, namely USBI.1 and USB2.0 [3].
The transfer rate of the high-speed mode of USBI.1 is 12Mbit/s, and the transfer rate of the low-speed mode is 1.5Mbit/s, 1Mb/s=8 Mbit/s, 12 Mbit/s=l .5 MB/s [3].
The USB2.0 specification is evolved from the USBI.1 specification. Its transmission rate reaches 480Mbit/s, which is converted into MB to 60MB/s, which is enough to meet the rate requirements of most peripherals. The Enhanced Host Controller Interface (EHCI) in USB2.0 defines a framework compatible with USB1.1, which can drive USB.1 devices with USB2.0 drivers. That is to say, all devices that support USB1.1 can be used directly on the interface of USB2.0 without worrying about compatibility issues, and accessories such as USB cables and plugs can also be used directly [3] .
The USB2.0 standard further increases the interface rate to 480Mbit/s, which greatly shortens the transmission time of video and audio files in LCD color TVs [3] .
Type-C interface
Type-c is an interface type that can be applied to both PC (master device) and external devices (slave devices, such as mobile phones), which is epoch-making [7].
Micro-USB interface
Micro-USB is a USB2.0 standard interface, the version of Mini-USB.
Its characteristics are as follows [8]:
Micro-USB connectors are smaller than standard USB and Mini-USB connectors, saving space [8];
With up to 10,000 times of insertion and extraction life and strength [8];
Blind insertion structure design [8];
Compatible with USB1.1 (low speed: 1.5Mbit/s, full speed: 12Mbit/s) and USB2.0 (high speed: 180 Mbit/s) [8];
At the same time provide data transmission and charging [8].