1. Batch processing: In order to let more people use computers, batch processing system appeared. The so-called batch processing refers to the way that user programs and data are pre-loaded into tapes or tapes and read by computers in a certain order, so that these programs and data to be executed by users can be processed in batches together. 2. Time-sharing system: After batch processing system, time-sharing system appeared in 1960s. It refers to a system in which multiple terminals are connected to the same computer, allowing multiple users to use a computer at the same time. This also reflects an important feature of time-sharing system-exclusiveness (the important features of time-sharing system include reusability, exclusiveness, interactivity and timeliness). 3. Communication between computers: In the 1970s, the performance of computers developed rapidly, the volume tended to be miniaturized, and the price dropped significantly. So the computer began to enter the enterprise to deal with daily affairs. In order to improve work efficiency, people began to study the communication technology between computers. 4. The emergence of computer networks: In the 1980s, a network was born that could interconnect all kinds of computers. It can connect all kinds of computers, from large supercomputers or mainframes to small personal computers. 5. Internet popularization: In the 1990s, companies and universities focusing on information processing have allocated a computer to each employee or researcher, forming a "one person, one computer" environment. However, the construction of this environment is not only expensive, but also will encounter many new problems in the process of use. This is also the reason why people began to "slim down" later (personal computers and UNIX workstations are as good as mainframes in performance. Coupled with the continuous improvement of the network functions of personal computers and UNIX workstations, it is more advantageous to build networks with these devices than with mainframes, mainly in two aspects: simple operation and low price. This has also triggered a new trend aimed at reducing the cost of network architecture. This trend is called slimming) and "multi-vendor connection" (connection between heterogeneous computers). Its purpose is to establish a lower-cost network environment by connecting computers from different manufacturers. The communication network technology connecting heterogeneous computers is the internet technology we see now. 6. The era centered on Internet technology: The popularity and development of the Internet have indeed had a tremendous impact on the communication field. 7. From "simple connection" to "secure connection": The convenience of the Internet has also brought negative problems to people's lives. Computer virus invasion, information leakage, online fraud and other criminal acts using the Internet are also increasing.