PC Interpretation 14: The Development of System Bus

Detailed history of system bus, including early PC bus and ISA bus, PCI/AGP bus, PCI-X bus and mainstream pciexpress, hypertransport High Speed Serial Bus. From the PC bus to the ISA and PCI bus, and then from the pci to the pciexpress and hypertransport systems, the computer has also completed three leaps in the three major turning points. In response to this process, computer processing speed, implemented functions, and software platforms are all undergoing the same evolution. Obviously, there is no progress in bus technology as the basis, the rapid development of computers cannot be discussed. The industry has a brand new starting point: pciexpress and hypertransport have created a nearly perfect bus architecture. The desire for high-speed bus in the industry is also endless. Both pciexpress2.0 and hypertransport3.0 will be put on the agenda, and they will bring about another improvement in efficiency. In computer systems, all functional components exchange data through the system bus. The speed of the bus has a great impact on the system performance. Because of this, bus is known as the nerve hub of computer systems. However, bus technology is much slower than CPU, video card, memory, hard disk, and other functional components. In the history of PC development over the past 20 years, the bus has only been updated three times, but every change in the PC has brought a new look to the computer.

What is system bus?
The system bus is also called an internal bus or a board-level bus. Because the bus is used to connect various functional components of the microcomputer and form a complete microcomputer system, it is called a system bus. The system bus is the most important bus in the microcomputer system. Generally, the microcomputer bus refers to the system bus, such as PC bus, at bus (ISA bus), and PCI bus.

How the system bus works
The position of the system bus in the microcomputer, such as the same person's central nervous system. The CPU reads and writes the memory content through the system bus, and writes the data in the CPU to peripherals through the bus, or the CPU is read from the peripherals. All micro-computers use bus structures. A bus is a group of communication lines used to transmit information. The Microcomputer connects all components through the system bus to realize information exchange between components in the microcomputer. Generally, the signal provided by the CPU needs to form a circuit through the bus to form a system bus. The system bus is divided into address bus, data bus, and control bus according to the function of transmitting information. These buses provide connections between the microprocessor (CPU) and memory and input/output interface components. It can be considered that a microcomputer is centered on the CPU, and all other components are mounted to the system bus connected to the CPU. This bus structure makes it easy to form a microcomputer. People can connect memory and interfaces of different sizes to the system bus according to their own needs, and it is easy to form a microcomputer of various sizes. In essence, a microcomputer connects the CPU, memory, and input/output interface circuits to the system bus correctly, the hardware design of computer application systems is essentially a problem of bus interface circuit design between external devices and the system bus. This bus structure design is a characteristic of computer hardware systems.

 

Composition of System Bus
The system bus in mainstream PCs are mainly composed of Front-End bus, storage bus, AGP bus, and PCI/PCIe bus. They are all connected to the North Bridge. The front-end bus connects the CPU and the North Bridge, which is the only entry for external data to enter the CPU. The CPU is connected to the master memory and video card through the North Bridge, and the PCI Controller is connected to the IO Device on the PCI bus through the North Bridge.