Restudy the principles of computer composition (1)-von Neumann structure

Background introduction

The first general-purpose electronic computer ENIAC

EDVAC -> Von Neumann’s draft report on EDVAC is the beginning of Von Neumann’s structural computer

EDSAC

UNIVAC

Von Neumann structure points

In the "EDVAC Design Draft" signed by von Neumann, the main points of the design of the computer structure are discussed

The computer should be composed of 5 parts : arithmetic unit, controller, memory, input device and output device
Data and programs are stored in the memory in the form of binary code without distinction , and the storage location is specified by the address of the memory
The computer can automatically fetch instructions from the memory for execution when it is working

Before EDVAC, such as the ENIAC computer, the decimal system was used, and the calculation program was realized by switch wiring. Von Neumann proposed that the program should be stored in the memory, and should not be realized by a switch connection. This is the concept of a stored program

Von Neumann structure and modern computers

analogy

The working principle of von Neumann structure computer

Remaining extensions

Computer operation analogy

Simplified model of computer structure

Memory
Controller
Arithmetic unit

The overall structure of the model machine

The process of computer execution

Instruction format:ADD R0, [6]

Indicates that the contents of general register R0 and the contents of the storage unit at address 6 are added

The result of the operation will be written back to the first operand by default, namely R0

Computer input and output

The concrete realization of von Neumann structure

The main components of von Neumann computer

When the computer starts, it accesses the read-only memory BIOS chip through the north bridge and the south bridge. Strictly speaking, BIOS does not belong to the memory part, but belongs to the external recording medium, just like the punched paper tape of early computers.

North-South Bridge Architecture

The red arrow indicates the channel with high transmission pressure, and the green arrow indicates the channel with relatively low transmission pressure

Since the CPU's access to the main memory is the bottleneck of the system, the main memory controller in the North Bridge is then moved to the CPU, which greatly improves the speed of the CPU's access to the main memory.

In addition to the access to the CPU and main memory, the next thing to be solved is the access of the CPU and the graphics card, so in the subsequent evolution, the PCIe controller is also included in the CPU. In this way, some of the most important components in the north bridge have been integrated into the CPU, so there is no need for the north bridge to exist. Thus, after integrating the remaining functions in the north bridge with the south bridge chip, the north-south bridge architecture disappears. The motherboard of a personal PC has been reduced from a three-piece structure to a two-piece type. Since there is no North Bridge, the name South Bridge sounds strange, so I renamed it PCH