Computer Bus

Computer Bus

Data Bus | Address Bus | Control Bus

Bus Architecture | Bus Width | Bus Speed

The Computer Bus is a communication link  used in a computer system to send the data , addresses , control signals and power to various components in a computer system.

The computer buses are used to connect the various hardware components that are part of the computer system.

In simple words , the computer buses are electrical wires which connect the various hardware components in a computer system . The computer bus carries the data , control signals , other information and  the power supply to these components.

The computer system makes use of different types of buses such as data bus , address bus and control bus.

What Is Computer Bus ?

In this article, we are going to study in detail what are computer buses , the computer system bus architecture ,  types of buses , technical features and the functions of the computer buses.

Computer Bus

Table Of Contents

What Is Computer Bus ?

The  computer system  consist of  number  of  internal  and  external components . These components  are physically  interconnected  and communicate with each other through a network of  wires running  across the computer system.

These  wires are referred as computer buses . The buses are  essential  to the functioning  of  the computer  system.

The computer  buses can be in the form of wired cables  or  electrical 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 computer system bus architecture , technical features of these buses  such as bus width  and bus speed  and its overall impact  on  the  system  performance.

Computer System
Computer Components

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  the 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  computer system  performance . The bus width and the bus speed affects the system performance .

Computer Bus

Types Of Computer Buses

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 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  bus And External bus ).
  • Connectivity with the CPU  chipset (  Through  Northbridge  Or  Through Southbridge ) 

Bus Types On the 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.

Computer Bus Types

Computer Bus System

Bus Types Based On the 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 Types Based On The 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  

Computer Bus

Data Bus

In computer architecture , the data bus is  a wired connection dedicated for transmitting the data between the CPU , peripheral devices and other hardware 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  can carry at a time.

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.

Computer Bus

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 the 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 transmits the control signals such as device interrupt signal , byte enable signal , memory read or write signals  and  status signals.

Control Bus

How CPU Works ?

Address Bus

What Is A Address Bus ?

The computer program consist of number of program instructions. These instructions direct the CPU to perform desired operation. 

The operating system loads the program instructions and the data into the main memory . The  CPU  executes the program instructions one-by-one by  fetching  the  program instructions  from  the  main  memory  RAM  ( Random Access Memory )  .

 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” along with the data bus and the control bus which we have discussed .

How CPU Works

System Bus

What Is A System Bus ?

System Bus is the main bus which contains Data Bus , Address Bus And Control Bus. 

The System bus in computer system  connects  number of vital internal hardware components placed on the motherboard .

These hardware components   mainly include  CPU , motherboard , Internal  add on cards  such as  Graphic card , Sound card  , Network card ,  RAM ( Main Memory ) and the 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. The System bus  transfers   data , memory   addresses  and  device control  instructions.

What Is System Bus

Computer Bus

Computer Architecture

Computer Bus Functions

What Are The Functions Of The Computer Bus ?

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. 

  1. Data Sharing .
  2. Addressing
  3. Control  Signals
  4. Providing Power to Components .
  5. Sharing The System Time .
Computer Bus Types And Functions

The internal buses connect the various internal system components such as microprocessor ( CPU ) , RAM ( main memory ) , Chipset ( North Bridge And South Bridge ) and disk memory ( Hard Disk ) .

The external bus connects the various external system components such as monitor , keyboard , printer , external hard disk and other components externally connected to the system.

The system bus connects the most important internal system components such as Microprocessor ( CPU ) and main system memory RAM . The system bus is also referred as FSB ( Front Side Bus ) or memory bus. It consist of data bus , address bus and control bus.

The expansion bus connects the most important internal system components such as Microprocessor ( CPU ) and PCI OR PCI Express slots on the motherboard .

The PCI And PCI Express slots are used to connect the add on cards such as graphics card and sound card . These cards are installed to enhance the system performance.

The input and output bus connects the most important internal system components such as Microprocessor ( CPU ) , main system memory RAM and the input / output devises through input and output controller south bridge

Front Side Bus And Back Side Bus

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 computer system at the hardware level understands only binary 0 ( zero ) and 1 ( one ) . And therefore , all computer programs are compiled to convert into machine code instructions in binary which computer CPU can decode and execute.      

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 at a time  through  these  buses .

Why Computer Bus Use Binary ?

Bus Width

What Is 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

What Is 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   ( CPU , main memory RAM , Graphics Card ) are connected through North Bridge. 

And other peripheral devices ( Display monitor , printer , keyboard , mouse ) are connected through the input & output controller chip South Bridge.

All these components are connected  by  using  the system of bus wires  which  essentially carries  three different types  of  information : 

1. Memory Addresses , 2. Control Instructions And  3. Data.

Expansion Bus

What Is 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 the  expansion cards .

Front Side Bus

What Is Front Side Bus ( FSB ) ?

The front side bus ( FSB ) represents one of the most important communication bus that connects some of the most vital components of the system. And hence , the FSB is also referred as system bus.

The front side bus connects the computers central processing unit ( CPU ) with the main system memory RAM . The FSB also connects PCI slots and DIMM slots on the motherboard with the processor socket .

And therefore , the FSB is an important communication bus that connects some of the most important components such as CPU , main memory RAM , graphics card and other components connected through PSI slots.

These components are connected using  the FSB through one of the memory controller chip called the north bridge. The motherboard chip set consist of two controller chips.

The front side bus is present on the motherboard embedded as a printed circuit board ( PCB ) wired connections running across the motherboard PCB .

The FSB speed is considered as an important parameter that significantly affect the CPU performance . The FSB speed is measured in Megahertz ( MHz ).

The FSB speed is generally ranges between 66 MHz to 800 Mhz. It can also be expressed as a ratio to CPU speed.

RAM Standard

RAM FSB Speed

RAM Code

DDR

100 MHz

PC - 1600

DDR

266 MHz

PC - 2100

DDR

333 MHz

PC - 2700

DDR

400 MHz

PC - 3200

DDR2

400 MHz

PC2 - 3200

DDR2

533 MHz

PC2 - 4200

DDR2

667 MHz

PC2 - 5300

DDR2

800 MHz

PC2 - 6400

DDR2

1066 MHz

PC2 - 8500

DDR3

800 MHz

PC3 - 6400

DDR3

1066 MHz

PC3 - 8500

DDR3

1333 MHz

PC3 - 10600

DDR3

1600 MHz

PC3 - 12800

DDR3

1867 MHz

PC3 - 14900

DDR4

1867 MHz

PC4 - 14900

DDR4

2133 MHz

PC4 - 17000

DDR4

2400 MHz

PC4 - 19200

DDR4

2666 MHz

PC4 - 21300

DDR4

4000 MHz

PC4 - 32000

The front side bus ( FSB )  is bi-directional bus . The FSB is used to by the CPU to either receive or send the data from various components connected to the CPU.

 The CPU frequently communicates with system main memory RAM and other devices during the program execution. And therefore , the FSB speed matters for the CPU performance.

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