Bus

A bus is a subsystem that is used to connect computer components and transfer data between them. For example, an internal bus connects computer internals to the motherboard.

A bus may be parallel or serial. Parallel buses transmit data across multiple wires. Serial buses transmit data in the bit-serial format.

Parallel bus standards include advanced technology attachment (ATA) or small computer system interface (SCSI) for a printer or hard drive devices. Serial bus standards include the universal serial bus (USB), FireWire or serial ATA with a daisy-chain topology or hub design for devices, keyboards or modem devices. 

Computer bus types are as follows:

• System Bus: A parallel bus that simultaneously transfers data in 8-, 16-, or 32-bit channels and is the primary pathway between the CPU and memory.

• Internal Bus: Connects a local device, like internal CPU memory.

• External Bus: Connects peripheral devices to the motherboard, such as scanners or disk drives.

• Expansion Bus: Allows expansion boards to access the CPU and RAM.

• Frontside Bus: Main computer bus that determines data transfer rate speed and is the primary data transfer path between the CPU, RAM, and other motherboard devices.

• Backside Bus: Transfers secondary cache (L2 cache) data at faster speeds, allowing more efficient CPU operations.

A bus was originally an electrical parallel structure with conductors connected with identical or similar CPU pins, such as a 32-bit bus with 32 wires and 32 pins. The earliest buses often termed electrical power buses or bus bars were wire collections that connected peripheral devices and memory, with one bus designated for peripheral devices and another bus for memory. Each bus included separate instructions and distinct protocols and timing.