Computer Bus
Computer Bus is a communication link used in a computer system to send Data , Addresses , Control Signals And power to various components within a computer system.
Computer Buses
Table Of Contents
What Is Computer Bus ?
The computer system consist of number of internal and external components . These components are physically inter connected and communicate with each other , through a network of wires running across the computer system . These wires are referred as buses and are essential to the functioning of the computer system .
The computer buses can be in the form of cables or wires embedded in the computer motherboard PCB ( Printed Circuit Board ) visible on the rear side of motherboard . It is important for computer science professional to study the technical features of these buses such as bus width and bus speed and its overall impact on the system performance of a computer system.
A bus is a common communication pathway used in a computer system through which information flows from one computer component to another. The computer bus system is a network of buses which physically connect all the components with wires ( actual bus wires OR circuit wires on the motherboard ) . The bus system consist of different types of buses depending upon the components being connected and function assigned to the bus .
A bus can consist of set of wires grouped together as connection wire or a printed circuit boards which carry the data and other commands ( instructions ) from the CPU to the memory and to various other components connected to the system . The bus performance is an important parameter to access the system performance .
Types Of Computer Bus
The computer bus system makes use of different types of buses depending upon the purpose and the function of the bus . The computer system buses can be classified on the basis of type of number of factors . These factors include :
- Components being connected . ( CPU , RAM , Input And Output Devices ).
- Type of Data being Transmitted ( Data , Address , Control Signals ) .
- Location of the components ( Internal And External ).
- Connectivity with the CPU ( Through Northbridge Or Through Southbridge )
Bus Type On Data Being Transmitted
The computer system buses can be classified on the basis of type of the data being transmitted as :
1. Data Bus , 2. Address Bus , 3. Control Bus.
Bus Type On Components Being Connected
The computer system buses can be classified on the basis of type of the components being connected as :
1. System Bus , 2. Expansion Bus , 3. Input And Output Bus.
Bus Type On Location Of Components
The computer system buses can be classified on the basis of location of the component being connected as :
1. Internal Bus , 2. External Bus
Data Bus
In computer architecture , the data bus is a wired connection dedicated for transmitting the data between the CPU and other components . The data bus is a part of the system bus in addition to address bus and control bus .
A data bus has many different features , but one of the most important feature is the bus width . The width of a data bus refers to the number of bits ( electrical wires ) that the bus is can carry . The Common data bus widths include 8 bit , 16 bit , 32 bit and 64 bit . The wider the bus width , faster would be the data flow on the data bus and thus better system performance.
Control Bus
The CPU ( Microprocessor ) contains a control unit which controls the functioning of all other components connected to the computer system . The control bus is used to transfer the control signals from one component to another component .
A control bus is a computer bus that is used by the CPU to communicate with devices that are connected to the computer system. These devices are connected with the help of cables and printed circuits board such as motherboard. The Control Bus is a part of System Bus in addition to Data Bus and Address Bus.
The Central Processing Unit ( CPU ) transmits different types of control signals to the system components. The devices also communicate with CPU by transmitting the control signals using the control bus.
The control bus is a bidirectional and assists the CPU in synchronizing control signals to the internal components and the external devices connected to the system. The control bus transmit control signals such as device interrupt signal , byte enable signal , memory read or write signals and status signals.
Address Bus
The computer program consist of number of program instructions. These instructions direct the CPU to perform desired operation. The CPU executes the program instructions one-by-one by fetching the instructions from the main memory RAM .
In order to perform the memory read or write operation from the main memory RAM , the CPU sends either read or write control signal on the control bus and address of the memory location along the “Address Bus” from where the operation is to be performed . The address bus is a part of the “System Bus” .
System Bus
A System Bus is a main bus which contains Data Bus , Address Bus And Control Bus. The System bus in computer system connects number of internal components which mainly include CPU , motherboard , Internal add on cards such as Graphic card , Sound card , Network card , RAM ( Main Memory ) and internal hard disk .
A system bus is a set of parallel wires which connects the two or more independent major internal components of a computer system. System bus transfers data , memory addresses and device control instructions.
Computer Bus Functions
The computer bus system makes use of different types of buses . Each of these bus is assigned to carry specific type of signal and data depending upon its function.
- Data Sharing .
- Addressing
- Control Signals
- Providing Power to Components .
- Sharing System Time .
Computer Bus And System Performance
Computer Bus Width And Bus Speed
A bus is a information highway over which information flows and wider the bus , the more information can flow over the channel . And therefore , a compatible bus width and bus speed is important for the optimal performance of the two most vital system components which includes Central Processing Unit ( CPU ) and main system memory RAM.
This is similar to a multi lane wider highway that can carry more cars due to more number of lanes available for traffic . whereas , a single lane road can carry less number of cars as compared to a multi lane road .
The bus consist of group of cables and each of these cable can carry 1 BIT ( Binary 0 OR 1 ) at a time . Therefore a bus consist of a group of cables so that a group of bits can be sent through the bus .
Bus Width
The size of a bus is measured in terms number of Bits it can transmit at a time . Each wire can transmit one bit thus more number of wires in the bus can transmit more bits at a time . This number of wires in bus is referred as Bus Width.
The Bus width is an important measure because it determines how much data can be transmitted at one time. For example, a 16 Bits bus can transmit 16 bits of data and a 32 Bit Bus can transmit 32 bits of data at a time.
The bus consist of group of cables and each of these cable can carry 1 BIT ( Binary 0 OR 1 ) at a time . Therefore a bus consist of a group of cables so that a group of bits can be sent through the bus .
This is similar to a multi lane wider highway that can carry more cars due to more number of lanes available for traffic .
Bus Speed
The Bus performance is important for optimal CPU performance . The Bus performance is measured on two factors ( Bus Width And Bus Speed ) . The bus speed is another important parameter for the bus performance . The bus speed is defined by its frequency expressed in Hertz .
The bus frequency is the number of data packets sent or received per second. Each time that data is sent or received , It is called as one cycle. The bus speed is generally referred to the FSB – Front Side Bus speed . The Front Side Bus connects the CPU to the memory controller chip North-bridge .
What Is Bus Bandwidth ?
Let us summarize the bus width and bus speed using the highway analogy. If the bus width is the number of lanes available for traffic and the bus speed is how fast the vehicles are moving on each of these lanes .The bandwidth is the product of Bus Width And Bus Speed and reflects the amount of traffic that the channel can convey per second.
Motherboard Bus Architecture
The CPU is connected to the internal system components ( RAM , Graphics Card Network card ) and external peripheral devices ( Monitor , Printer , Mouse , Keyboard ) by using device controller circuits placed on the motherboard .
All the device controller chips are now integrated into only two controller chips called chip-set . The chip-set consist of two prominently visible IC Chips called North-bridge and South-bridge placed on the motherboard .
The memory controller chip North-bridge and input / output controller chip South-bridge circuits are placed on the motherboard. The internal components are connected through North Bridge and other peripheral devices are connected through South Bridge. All these components are connected by using a system bus wires which carries three types of information
1. Memory Addresses , 2. Control Instructions And 3. Data.
Expansion Bus
The performance features and functionality of a computer system can be extended by adding an additional cards such as graphics card Or sound card.
The expansion slots are the ports located on the motherboard of a computer system in which an expansion cards can be installed . The user can use these slots to insert additional expansion cards as per the functional requirements .
An expansion bus is a group of wires OR PCB used to connect with the expansion slots on the motherboard. These expansion slots are used for installing expansion cards .
