"According to Moore's Law, the number of transistors and resistors integrated into a chip doubles every two years, and the performance of CPUs (central processing units) and DRAM (main memory) is increasing rapidly. However, while the DRAM storage capacity increases, the read speed cannot be increased simultaneously, resulting in a great mismatch with the CPU frequency, which will greatly affect the overall performance of the entire microprocessing system.

In my opinion, one of the main problems in CPU design is to solve the balance between high-speed CPU and low-speed DRAM in order to improve the overall performance of the system. Adding a cache between them can effectively solve this problem. In fact, as early as 1964, the concept of caching appeared in the system/360 system, a mainframe computer system launched by IBM......"

This is a small academic salon held in the living room of Professor Zhao Weiming's home, and every weekend afternoon, a group of students and teachers who love electronic technology gather on the sofa in the living room of Professor Zhao's house to talk freely. Professor Zhao is also happy to visit small gatherings like guò to broaden students' horizons and cultivate their professional interests.

Today's topic is the development direction of microprocessors, Li Xuan is invited for the first time, and he has been a good listener since the beginning. He was the only one in the room who was not born in electronics and chose to major in electronic computing.

CUHK's electronics major mainly focuses on hardware, while electronic computing studies are later computer majors, mainly learning software knowledge such as programming languages and number structures, although the two are related, but in fact, they are two completely different directions.

Li Xuan, who was born to learn software, always joins in the fun of hardware people. Zhao Weiming was also a little curious about him, a maverick student, and took this opportunity today to speak by name, to test how much ink he had in his stomach as an interesting student in Cao Ying's heart.

Li Xuan thought about it in his heart for a long time before talking about his opinion. His views can't be too detailed and too deep, it's only been a month since the start of school, and the advanced course of electronics is not even an introduction for a freshman like him. But it can't be said without substance, after all, the purpose of his coming to the party is to show his strength and lay the foundation for establishing his image as a technical cow in the future.

In addition to these, he also had to be careful not to pop up some terms that did not exist in this era, such as the term non-blocking caching seems to have only been proposed in the paper in the 80s, and victim caching only began to be studied in the 90s.

With the vigorous development of microprocessors in the seventies, the problem of slow memory read speed has become more and more prominent. This problem was not obvious in the era of eight-bit processors, and with the release of Intel's sixteen-bit 8086 processor, this problem has begun to slowly appear.

Li Xuan remembers that in 1985, when Intel released the first 32-bit 80386 processor, it had already used external caches to solve the problem of memory speed bottlenecks. Therefore, his view is very much in line with the next development trend of mainstream processor technology, and it is more forward-looking.

Zhao Weiming sat on the side and sipped coffee, and couldn't help but nod slightly after listening to Li Xuan's point of view. Before he returned to Hong Kong Chinese University to teach, he was originally engaged in microprocessor development at RCA, and he participated in the core research and development of RCA's only famous microprocessor RCA1802 that has left a name in history.

This eight-bit processor is known as the originator of the RISC (Reduced Instruction Set) processor, which has low power consumption, strong reliability, and can meet the harsh environment of high radiation in outer space, and is the first microprocessor to be used in space.

NASA's Voyager 1 spacecraft, launched in 1977, used three 1802 processors as the core of the system. Before Li Xuan's rebirth, this probe farthest from the earth, after a long journey of more than 30 years, had successfully flown out of the solar system and into interstellar space, but it was still in normal working condition.

"I think RISC (Reduced Instruction Set) is the way to optimize computer instruction systems in the future. In the latest paper published by Professor Paterson of the University of Berkeley, a research team pointed out that the usage rate of various instructions varies greatly: 80% of the instructions used in a typical program operation process are the 20% of the commonly used instructions in the instruction set.

In order to balance the design of a large number of complex instructions that are rarely used in other places, we have greatly increased the complexity of the overall structure design of the CPU, which undoubtedly increases the time and cost of processor design on a large scale......"

When Li Xuan was talking, his face was filled with a focused and confident expression, unconsciously letting others focus on him. Zhao Weiming's gaze also fell on him again, with a slight imperceptible wry smile in surprise.

This is really a good seedling, although he is a freshman who has just entered the freshman, he is already able and likes to read the most cutting-edge academic journals in related majors, and the solid theoretical foundation shown from them is no worse than the two master's students who follow him. Li Xuan's occasional keen views gave him the illusion that he was standing in front of him talking and laughing as a professional prefacer who had been immersed in the field of electronics for more than ten years.

Knowledge and skills can be acquired, but vision and insight are gifted from God. Zhao Weiming felt that the piece of jade in front of him was the most surprising discovery he had made in the past few years, but when he thought that he was a student majoring in electronic computing research, he couldn't help but feel a little depressed in his heart.

Should I persuade him to switch to the electronics major? As for the choice of students' future majors, CUHK has always taken the position that it is up to the students' own preferences. After all, this is a matter related to the fate and future of the individual, and the teacher can give advice for reference, but he does not have the right to decide the future of the student.

Zhao Weiming decided to observe patiently for a while, after all, Li Xuan had just entered the university, and there were still more than two months left in the first semester, and he still had more than three years to think carefully. If Li Xuan is really talented in the field of electronics, he will not be excluded from engaging in this kind of work, and then he will personally go out to explain the stakes to the students.

Li Xuan also noticed Professor Zhao Weiming's surprised expression when he looked at him, and the smile on his face couldn't help but be a little better. He came here today to pretend, and he had been in the library for several days before, and professional journals were like books that other freshmen couldn't read, but for him, they were handy.

Comparing the papers in the journal, he had a general idea in his heart, which views have not yet been published in this era and cannot be said, and which views are hot spots in the near future.

And Li Xuan also successfully achieved his goal, which attracted the attention of Professor Zhao. Professor Chiu Wai Ming is the only professor in the Department of Electronics at CUHK who specializes in integrated circuit design and has practical experience in microprocessor design in large companies. He also has his own team at the school, specializing in the research of integrated circuits, especially microprocessors.

Except for CUHK electronics students, all the teachers and students who participated in the salon today were members of his research team. For example, sitting on the bamboo chair on the left, a man with a black and thin face, surnamed Cai, is the only PhD student in the Department of Electronics at CUHK. Dr. Cai is responsible for teaching "Introduction to Electronics", one of the compulsory courses for freshmen majoring in electronics.