What are Computer Buses?-Types of Computer Buses
A computer system consists of different devices. CPU must be able to communicate with all devices. The devices are connected together by a communications channel called a bus. A bus consists of set communication lines or wires. It is used to move a large number of bits in the form of electrical pulses from one unit to another.
The bus is used to connect the following units:
- Central Processing Unit (CPU)
- Control Unit
- Arithmetic and Logical Unit.
- Main Memory (RAM, ROM)
Input/ Output Devices
The bus is a common path to transfer data and commands between CPU, memory and input devices, and output devices. It is also used to send and receive data from secondary storage. The capacity of a bus depends on the number of data lines in it.
The amount of data that a bus can carry at one time is called bus width. A bus with 16 lines can carry 16 bits or 2 bytes at a time. A bus with 32 lines can carry 32 bits or 4 bytes at a time. System buses are part of the motherboard.
The speed at which data moves from one location to another is called bus clock speed. It affects the overall performance of the computer. Bus clock speed is measured in units of megahertz (MHz) or millions of clock cycles per second.
The data bus is the most common bus. It is used to carry data. It is an electrical path that connects the CPU, memory, input/output devices, and secondary storage devices. The bus contains a parallel set of lines.
The number of lines affects the speed of data transfer between different components. A data bus with more lines can carry more data. A data bus with 16 lines can carry 16 bits (2 bytes) of data. A bus with 32 lines can carry 32 bits (4 bytes) of data.
A bus is designed in such a way that it can communicate with the components efficiently. The buses in old computers could carry only one byte of data. The buses used today can carry multiple bytes at one time. It improves the speed and performance of the computer system.
The address bus is used to carry address information. It is a set of wires similar to the data bus. It only connects the central processing unit and memory. The following steps take place when the CPU needs data from the memory:
- CPU places the address of required data on the address bus.
- The address is carried to the memory.
- The data from the requested address is fetched and placed on the data bus.
- The data bus carries the data to the CPU.
The number of lines in the address bus determines the maximum number of memory addresses. If an address bus has 8 lines, the maximum number of memory locations that can be addressed is 28 = 256. The computers used today have32-bit address lines. These computers can access 4GB of memory.
The control bus is used to transmit different commands from one component to another component. For example, if the CPU wants to read data from the main memory, it uses a control bus to send the memory read command to the main memory of the computer.
The control bus is also used to transmit control signals like ACKS (Acknowledgement signals). A control signal contains the following:
Timing Information: It specifies the time for which a device can use data and address bus.
Command Signal: It specifies the type of operation to be performed.
Suppose that CPU gives a command to the main memory to write data. The memory ends an acknowledgment signal to the CPU after writing the data successfully. CPU receives e signal and then moves to perform some other action.