computer Buses structures in details with schematic diagram | types and functions of System bus

النواقل buses على جهاز الكومبيوتر

The purpose of the buses

The purpose of the buses on a computer is to reduce the number of "paths" required for communication between the components of the latter, for example between the processor and the chipset, or what is called the northbridge, and this is by making all communications over one data channel. This is why the "data highway" metaphor is used.

The data bus is characterized by the amount of information that can be transmitted at once. This amount, expressed in bits, corresponds to the number of physical lines on which data is transmitted simultaneously. A 32-wire mapped cable can transmit 32 bits in parallel. The term width is used to denote the number of bits that this bus can move at once.

 In addition, the conversion speed of this data is defined by its frequency (expressed in Hertz), and the number of data packets sent or received per second. Every time data is sent or received it is called a cycle. In this way, the maximum bus speed, or the amount of data that can be transferred per unit of time, can be found by multiplying its width by its frequency. For example, a bus that is 16 bits wide and at 133 MHz has a transmission speed equal to:

16bits * 133000000hz = 2128000000

In fact, each bus generally consists of 50 to 100 distinct physical lines, divided into three sub-groups. The first is the adress bus (sometimes called the memory bus), which transmits the memory addresses that the processor wants to access in order to read or write data. It is a unidirectional vector. The second is the data bus, which transmits the instructions received from the processor. It is a bidirectional two-way carrier. The third is the command bus, or command bus, that transmits requests and clocks from the control unit. It is a bidirectional vector, because it also transmits status words from the device toward the processor.

It is worth noting that for the correct communication between these complex electronic elements, there must be the same width for the buses or buses in charge of this. This explains why RAM modules sometimes had to be installed in pairs (for example, the first Pentium chips, which were 64-bit processor vectors, required two memory modules with each width at 32 bits).

Types of buses, the basic buses on the motherboard

There are generally two buses within a computer. The first one is the processor and it is called the front side bus or FSB for short.

 The internal bus allows the processor to communicate with the main system memory (RAM). The second which is sometimes called the I / O bus allows various components of the motherboard from USB, serial port, parallel port, RJ45 port, inserted cards PCI connectors, hard drives, CD drives, etc. to communicate with each other.

Our speech was printed on the vectors by a computer. Its meaning will not be complete if we do not speak in parallel on the chipset, for which I will devote a separate topic, God willing.


It is the component that routes data between buses of a computer, so that all the components that make up a computer can communicate with each other. This chip or electronic chip was originally made of a large number of electronic chips, hence the name. It generally has two components. The first is the NorthBridge (also called the memory controller) that is responsible for controlling the transfers between the processor and the RAM, which is why it is physically located near the processor. Sometimes called GMCH, for graphic control board and memory. The second is SouthBridge (also called I / O control unit or expansion control unit), which deals with communications between other devices as mentioned before. Also called ICH.

The term bridge is generally used to designate a component that connects two different buses or transporters:

In a computer, a bus is defined as a set of physical connections (such as cables, printed circuits, etc.), which can be shared by multiple hardware components in order to communicate with each other.