The computer system structure adopts the "Von Neumann" structure. The von Neumann structure, also known as the Princeton structure, is a memory structure that combines program instruction memory and data memory. It uses binary logic, program storage and execution, and the computer is composed of five parts (operator, controller, memory , input device, output device); the characteristics of this structure are "program storage, shared data, sequential execution", which requires the CPU to retrieve instructions and data from the memory to perform corresponding calculations.
The operating environment of this tutorial: Windows 7 system, Dell G3 computer.
The current mainstream computer system structure adopts the "Von Neumann" structure.
The Von Neumann structure, also known as the Princeton structure, is a memory structure that combines program instruction memory and data memory. The program instruction storage address and the data storage address point to different physical locations in the same memory, so the width of the program instructions and data are the same. For example, the program instructions and data of Intel's 8086 central processor are both 16 bits wide.
The mathematician von Neumann proposed three basic principles for computer manufacturing, namely the use of binary logic, program storage and execution, and the computer is composed of five parts (operator, controller, memory, input device, output device), this theory is called the von Neumann architecture.
Development History
Before the birth of computers, people had bottlenecks in the accuracy and quantity of calculations. For computers like this The demand for machines was very strong, and von Neumann's logic and computer ideas guided him to design and build the first general-purpose electronic computer in history. His computer theory is mainly influenced by his own mathematical foundation and is highly mathematical and logical. He generally calls this theory "the logical theory of computers". His idea of computer stored programs was another of his great innovations. By placing stored programs in internal memory, he successfully solved the problems of too small computer storage capacity and too slow computing speed at that time.
During World War II, the U.S. military required laboratories to provide it with computationally intensive calculation results. So there was the idea of developing an electronic computer. Faced with this demand, the United States immediately formed a research and development team, including many engineers and physicists, to try to develop the world's first computer (later called the ENIAC machine). Although the most advanced electronic technology is adopted, there is a lack of principle guidance. At this time, von Neumann appeared. He brought up a crucial aspect: the logical structure of computers. Von Neumann started with logic and led the team to improve ENIAC. His logic design has the following characteristics:
(1) Separate the circuit and logic designs to create optimal conditions for computer construction;
(2) Combine the personal nervous system and computer Combined together, a new concept is proposed, namely biological computers.
Even though the ENIAC machine was realized with the top technology in the United States and even the world at that time, it used temporary storage and determined the arithmetic unit as the foundation. Therefore, it had many shortcomings, such as limited storage space, inability to store programs, etc., and the operation The speed is slow and inherently irrational. Von Neumann formulated the following optimization plan based on this premise:
(1) Use binary to perform operations, which greatly speeds up the computer;
(2) Store the program, that is, through the computer Internal memory stores calculation programs. In this way, programmers only need to write relevant computing instructions through the memory, and the computer can immediately perform computing operations, greatly speeding up computing efficiency.
Von Neumann structural diagram
Features
The basic structural form followed by the development of modern computers It is always a von Neumann machine structure. The characteristics of this structure are "program storage, shared data, and sequential execution", which requires the CPU to retrieve instructions and data from the memory to perform corresponding calculations. The main features are:
(1) Single processor structure, the machine is centered on the arithmetic unit;
(2) Adopts the idea of program storage;
(3 ) Instructions and data can participate in operations;
(4) Data is expressed in binary;
(5) Completely separates software and hardware;
(6) Instructions are represented by Composed of operation codes and operands;
(7) instructions are executed sequentially.
Limitations
The speed of information exchange between the CPU and shared memory has become the main factor affecting system performance, and the increase in information exchange speed is restricted by the speed of the storage element , memory performance and structure and many other conditions.
The stored program method of the traditional von Neumann computer architecture makes the system dependent on memory. The speed of the CPU accessing the memory restricts the speed of the system. The technical level of integrated circuit IC chips determines the performance of memory and other hardware. In order to improve the performance of hardware, chip manufacturing companies represented by Intel Corporation have made great efforts in integrated circuit production and have achieved great technical results. Now every 18 months, the integration level of ICs doubles, the performance doubles, and the product price drops by half. This is the so-called "Moore's Law." This pattern has lasted for more than 40 years and is expected to continue for several more years. However, two fundamental limitations faced by electronic products exist objectively: the speed of light and the atomic properties of materials. First of all, the speed of information propagation will ultimately depend on the speed of electron flow. The flow of electronic signals in components and wires will cause time delays. Too high a frequency will cause signal distortion, so the speed of components cannot be infinitely increased until it reaches the speed of light. Second, the electronic signals of the computer are stored in transistors represented by silicon crystal materials. The improvement in integration is that the transistors become smaller, but the transistors cannot be smaller than the volume of one silicon atom. As semiconductor technology gradually approaches the size limit of silicon processes, the rules derived from Moore's Law will no longer apply.
Analysis of the structural flaws of von Neumann computer architecture:
(1) Instructions and data are stored in the same memory, resulting in the system's over-reliance on memory. If the development of storage devices is hindered, the development of systems will also be hindered.
(2) Instructions are stored in the memory in the order of their execution, and the instruction counter PC specifies the unit address where the instruction to be executed is located. Then fetch the instructions to perform the operation task. So the execution of instructions is serial. Affects the speed of system execution.
(3) The memory is linearly addressed according to address access, and the address access is arranged in sequence, which is conducive to storage and execution of machine language instructions, and is suitable for numerical calculations. However, the memory represented by high-level language is a set of named variables. Variables are called by name and not accessed by address. There is a large semantic gap between machine language and high-level language, which is called the von Neumann semantic gap. Eliminating semantic gaps has become a major problem facing the development of computers.
(4) Von Neumann architecture computers were born for arithmetic and logical operations. Currently, they have reached high speed and accuracy in numerical processing, while the development of non-numeric processing applications is slow. A major breakthrough in architecture is required.
(5) The traditional von Neumann type structure belongs to the control drive method. It executes instruction codes to process numerical codes. As long as the instructions are clear and the input data is accurate, it will run automatically after starting the program and the results will be expected. Once there are errors in instructions and data, the machine will not actively modify the instructions and improve the program. However, much information in human life is vague, and the occurrence, development and results of events are unpredictable. The intelligence of modern computers cannot cope with such complex tasks.
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