What is BUS?
A bus is a collection of wires through which data is transmitted between various components of a PC. If we closely look at the motherboard, we can notice a network of golden electric paths etched on both sides of the motherboard. They form the bus of the PC. A bus acts as the system’s expressway – it transmits data between various components on the motherboard. Logically bus consists of two parts – an address bus and a data bus.
Data Bus: Data Bus is an electrical path that connects the CPU, memory & other hardware devices on the motherboard. Bus is a group of parallel wires. The number of wires in the bus can affect the speed at which data can travel between hardware components. Each wire can transfer one bit at a time. Therefore, an eight-wire bus can move eight bits at a time. A 16-bit bus can transfer two bytes and a 32-bit bus can transfer four bytes at a time. PC buses are designed to match the capabilities of devices attached to it. For e.g. a 32 micro processor must support 32 bit data bus.
Following are different types of data bus used in PCs.
- MCA bus – Micro Channel Architecture,
- EISA bus – Extended Industry Standard Architecture,
- ISA bus – Industry Standards Architecture,
- PCI bus – Peripheral Component Interconnect.
Address Bus: Address bus is also a set of wires, similar to the data bus. But it is used to connect CPU and RAM. Data bus always carries data but address bus carries memory addresses. Each byte in RAM is associated with a number, which is the memory address. To request data from RAM, CPU sends the required address.
The number of wires in address bus determines the maximum number of memory addresses. For example, one byte of data is enough to represent 256 different values. If the address bus could carry only eight bits at a time, the CPU could address only 256 bytes of RAM. Actually, most of the early PCs had 20-bit address buses, so the CPU could address 1 MB of data. Today, most CPUs have 32-bit address buses that can address 4 GB of RAM.
