There are two types of data transmission. These are as follows:
1. Parallel Transmission      2.    Serial Transmission

  1. Parallel Transmission

A method of transmission in which groups of bits are sent at the same time over multiple wires is called parallel transmission. It is usually unidirectional. Each bit is transmitted over a separate line.

The internal transfer of data in a computer uses a parallel mode. The data transmission between computer and printer is done using parallel transmission. Parallel transmission is faster because all bits are sent at the same time.

Parallel data transmission

Bit 0———————————————————–bit0









Sender                     media                       receiver

  1. Serial Transmission

A method of transmission in which data is sent one bit at a time is called serial transmission. The character bits are sent sequentially. Serial transmission is slower than parallel transmission as data is sent sequentially one bit at a time.

Telephone lines use this method of data transmission. Each individual bit of information travels along its own communication path.

Serial data transmission

Explain asynchronous and synchronous transmission.

Two types of data transmission are as follows:

  1. Asynchronous transmission.       2.    Synchronous transmission
  1. Asynchronous Transmission

In asynchronous transmission, data is transmitted character by character. There are irregular gaps between characters in this transmission. It is cheaper t implement because data is not saved before it is sent.

It uses a special start signal. The signal is transmitted at the beginning of each message. The start signal is sent when the character is about to be transmitted.

A start bit has a value of 0. It is called space state. The value of 0 indicates that a character is about to be transferred. It alerts the receiver and it gets ready to receive the character. If start bit has a value 1, it indicates that the line is idle. It is also called mark state.

data transmission

  1. Synchronous Transmission

In the synchronous mode, the saved data is transmitted block. Each block may consist of many characters. It uses a clock to control the timing of bits being sent. A large amount of information can be transmitted at a single time with this type of transmission.


Synchronous transmission is much faster than asynchronous because there is no gap between characters. This transmission is suited for remote communication between a computer and related devices like printers etc.