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Parallel versus serial communication. In data transmission, parallel communication is a method of conveying multiple binary digits simultaneously using multiple conductors. This contrasts with serial communication, which conveys only a single bit at a time; this distinction is one way of characterizing a communications link.
D 0 is received first via serial transmission. All bits are received simultaneously via parallel transmission. In telecommunication and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus.
Serial ports use two-level (binary) signaling, so the data rate in bits per second is equal to the symbol rate in baud. The total speed includes bits for framing (stop bits, parity, etc.) and so the effective data rate is lower than the bit transmission rate.
Parallel transmission is the simultaneous transmission of related signal elements over two or more separate paths. Multiple electrical wires are used that can transmit multiple bits simultaneously, which allows for higher data transfer rates than can be achieved with serial transmission.
At the destination, a second UART re-assembles the bits into complete bytes. Each UART contains a shift register, which is the fundamental method of conversion between serial and parallel forms. Serial transmission of digital information (bits) through a single wire or other medium is less costly than parallel transmission through multiple wires.
In general, parallel interfaces are quoted in B/s and serial in bit/s. The more commonly used is shown below in bold type. On devices like modems , bytes may be more than 8 bits long because they may be individually padded out with additional start and stop bits; the figures below will reflect this.
For example, on the original IBM PC, a male D-sub was an RS-232-C DTE port (with a non-standard current loop interface on reserved pins), but the female D-sub connector on the same PC model was used for the parallel "Centronics" printer port. Some personal computers put non-standard voltages or signals on some pins of their serial ports.
Today, the parallel port interface is virtually non-existent in new computers because of the rise of Universal Serial Bus (USB) devices, along with network printing using Ethernet and Wi-Fi connected printers. The parallel port interface was originally known as the Parallel Printer Adapter on IBM PC-compatible computers.