1. USB interface (Universal Serial Bus)

USB interface, as the most common and the most frequently used external interface of computer, has been born for more than 20 years. Since its launch in 1996, it has experienced several major versions of updates.

Different versions of USB are compatible with each other, so even the external device of USB2.0 can still be used on the interface of USB3.0. On the contrary, the device of USB3.0 can also be used on the interface of USB2.0, but the transmission speed is not so fast.

2. PS / 2 interface

As one of the oldest interfaces of computer, PS / 2 interface equipment is still in service. Now the only PS / 2 external equipment that can be seen is mouse and keyboard. PS / 2 interface is generally divided into purple (insert keyboard) and green (insert mouse).

And now the mouse and keyboard are generally using USB interface, after all, USB has a wider range of applications. Although the PS / 2 interface supports “hot swap” (only for the device loaded in the system), for the new device connected for the first time, it still needs to restart the computer to recognize it. In fact, the mouse and keyboard with PS / 2 interface are more compatible with old system devices than USB. In the face of debugging some old devices, we can only use PS / 2 interface to drive the mouse and keyboard. However, with the replacement of old devices, PS / 2 interface will eventually withdraw from people’s vision.

3. Ethernet interface

At present, the network interface used on personal computer is basically RJ-45 interface, with the highest transmission speed of Gigabit.

Generally, RJ-45 interface has two indicators: link indicator and act indicator.

4. Serial interface (COM interface), parallel interface (LPT)

The common serial interface is 9-pin serial port (DB9). On some old devices, DB9 looks like VGA interface, which is easy to be confused at first sight.

The working principle of serial interface is simple, mainly as one-to-one data transmission, such as debugging network equipment. The 25 pin parallel port is often used to connect printing equipment. But now few new devices provide serial / parallel ports, because the demand for work is getting smaller and smaller, and there is the popularity of USB interface. After all, the space of motherboard is so small, so it is more practical to save more USB interface.


ESATA interface is mainly used for external hard disk. From its name, we can see that it is also a kind of SATA serial interface specification. ESATA is an efficient and direct way to connect external hard disk, but now the USB mobile hard disk is more popular with consumers. It can be seen on some old laptops or external hard disk boxes.

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