Chapter 23

"According to Moore's Law, the number of transistors and resistors integrated on a chip will double every two years, and the performance of CPUs (central processing units) and DRAMs (main memory) is rapidly improving. However, while the storage capacity of DRAMs is increasing, the read speed cannot keep up, leading to a significant mismatch with the CPU clock frequency. This will inevitably greatly affect the overall performance of the microprocessing system.

I believe that one of the main issues in CPU design going forward is to address the balance between high-speed CPUs and low-speed DRAMs to improve the overall system performance. Adding a high-speed cache memory between them can effectively solve this problem. In fact, as early as 1964, the concept of cache appeared in the large computer system System/360 introduced by IBM..."

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

Today's topic is the development direction of microprocessors. Li Xuan was invited for the first time and has been a good listener from the beginning. Among the dozen or so people in the room, he is the only one who did not major in electronics but chose to study electronic computing.

The electronics major at Sun Yat-sen University mainly focuses on hardware, while electronic computing, which is the computer science major of the future, mainly focuses on programming languages and data structures, which are software-related knowledge. Although the two are related, they are actually two completely different fields.

Li Xuan, who studied software, often joins the hardware crowd. Professor Zhao Weiming is somewhat curious about this unconventional student and took the opportunity to call on him to speak today, to test how much knowledge this interesting student, who is in the wrong field, actually has.

Li Xuan carefully considered his response before sharing his views. His points cannot be too detailed or deep, as he has only been in college for a month, and the advanced course of electronics is far beyond the level of a freshman. However, he cannot speak without substance either, as his purpose in attending the gathering is to showcase his capabilities and lay the foundation for establishing a reputation as a technical expert in the future.

In addition, he must be particularly careful not to use terms that do not exist in this era, such as non-blocking cache, which was only proposed in the 1980s, and victim cache, which was only studied in the 1990s.

Therefore, Li Xuan chose the topic of high-speed cache. With the rapid development of microprocessors in the 1970s, the problem of slow memory read speed has become increasingly prominent. In the 8-bit processor era, this issue was not obvious, but with the release of Intel's 16-bit 8086 processor, the problem began to gradually emerge.

Li Xuan remembers that in 1985, when Intel released the first 32-bit 80386 processor, it already adopted an external high-speed cache to solve the memory speed bottleneck. Therefore, his views are very consistent with the mainstream development trend of processor technology and are quite forward-looking.

Professor Zhao Weiming, sitting on the side sipping coffee, nodded slightly after hearing Li Xuan's views. Before returning to teach at the Chinese University of Hong Kong, he was involved in microprocessor development at RCA. He participated in the core development of the RCA1802, the only famous microprocessor in RCA's history.

This 8-bit processor is hailed as the ancestor of RISC (Reduced Instruction Set Computing) processors. It has low power consumption and high reliability, capable of withstanding the harsh environment of outer space, making it the first microprocessor used in space.

In 1977, NASA launched the space probe "Voyager 1," which used three 1802 processors as the system core. Before Li Xuan's rebirth, this probe, the farthest from Earth, had successfully flown out of the solar system into interstellar space after more than 30 years of travel, but it is still functioning normally.

"I believe that RISC (Reduced Instruction Set Computing) is the future direction for optimizing computer instruction systems. A recent paper published by Professor Patterson's research team at the University of California, Berkeley, points out that the usage rates of various instructions are extremely uneven: 80% of the instructions used in a typical program are the 20% of commonly used instructions in the instruction set.

To balance the design of a large number of complex instructions that are rarely used, we have greatly increased the complexity of the overall CPU design, which undoubtedly significantly increases the time and cost of processor design..."

As Li Xuan spoke confidently, a focused and self-assured expression appeared on his face, inadvertently drawing the attention of the others to him. Professor Zhao Weiming's gaze also fell on him again, with a hint of surprise and a barely noticeable wry smile.

This is truly a good seedling. Although he is a freshman who just entered college, he is already able and enjoys reading the most cutting-edge academic journals in his field. The solid theoretical foundation he demonstrates is no less than that of the two master's students under his guidance. Li Xuan's occasional sharp insights give him the illusion that the person standing before him, talking confidently, is a professional with over a decade of experience in the electronics field.

Knowledge and skills can be cultivated later, but vision and insight are gifts from heaven. Professor Zhao Weiming feels that this piece of unpolished jade is his most pleasant discovery in recent years. However, thinking that Li Xuan is a student of electronic computing, a sense of frustration arises in his heart.

Should he persuade him to switch to the electronics major? The Chinese University of Hong Kong has always maintained the stance that students should choose their majors based on their own preferences. After all, this is a matter related to one's future and destiny. Teachers can offer advice and references, but they have no right to decide the students' futures.

Professor Zhao Weiming decided to observe Li Xuan for a while longer. After all, Li Xuan has just entered college, and the first semester still has more than two months left. He has more than three years to carefully consider. If Li Xuan truly has exceptional talent in the electronics field and is willing to work in this area, he can personally intervene and explain the pros and cons to the student when the time comes.

Li Xuan also noticed the surprised expression on Professor Zhao Weiming's face, and his smile grew even wider. He came today to show off, and he had spent several days in the library beforehand. Professional journals, which are like a foreign language to other freshmen, are easy for him to understand.

By comparing the papers in the journals, he had a rough idea of what to say. He knew which views had not yet emerged in this era and should not be mentioned, and which views were recent hot topics that he could use to show off, making a well-reasoned and forward-looking discussion.

Li Xuan successfully achieved his goal, drawing Professor Zhao's attention. Professor Zhao Weiming is the only professor in the electronics department at the Chinese University of Hong Kong who specializes in integrated circuit design and has practical design experience in microprocessors at major companies. He has his own team at the university, focusing on integrated circuit research, especially microprocessors.

Among the teachers and students participating in today's salon, besides the students majoring in electronics at the Chinese University of Hong Kong, the rest are members of his research team. For example, the man sitting on the left in a bamboo chair, with a somewhat dark and thin appearance and a middle part hairstyle, is surnamed Cai. He is the only doctoral student in the electronics department at the Chinese University of Hong Kong. One of the required courses for freshmen in the electronics major, "Introduction to Electronics," is taught by Dr. Cai.

---

Page AD begins

Page AD ends