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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 bit-serial format.
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.
Parallel bus standards include advanced technology attachment (ATA) or small computer system interface (SCSI) for printer or hard drive devices. Serial bus standards include 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: