Difference between Asynchronous and Synchronous

Key difference: Asynchronous and Synchronous are two different methods of transmission synchronization. The major difference between them lies in their transmission methods, i.e. Synchronous transmissions are synchronized by an external clock; whereas Asynchronous transmissions are synchronized by special signals along the transmission medium. 

The communication is synchronized in Asynchronous and Synchronous manner, through their respective signaling methods. These modes transfer the data from one destined source to the destination in order to carry out the communications. Broadly, asynchronous way of communication is an indirect way of communication which passes through various different modes of transformation; on the contrary synchronous way of communication s a direct way which connects to the receiver.

In Asynchronous data transfer mode, no common clock signal is present between the sender and receiver. The sender and receiver set ups a data transfer speed, which further at the time of transmission does not change and remains fixed. Both the sender and receiver set up their own internal circuits in order to access the data according to their agreement. The asynchronous communication and activities takes place outside of real time. It can be considered as the Asynchronous activities take place whenever the relevant user has time to complete them.

In Synchronous data transfer, the basic sender and receiver use the same clock signal. Hence, the sender and receiver receive the same clock signal, for this to happen a special type of clock signal is required. In the synchronous data transfer, the master or the main sender is supposed to provide the clock signal to all the receivers or recipients. The Synchronous communication works much like a phone call. Here, the Receiver must be available, otherwise the conversation cannot occur. The synchronous collaboration gives an immediate and spontaneous response from the desired receiver. Hence, this type of collaboration is considered to be ideal.

Hence, it can be concluded as both asynchronous and synchronous differ in their signaling and communication patterns. Synchronous types receive the sent clock signal only, while the asynchronous type receives the synchronization signal which is provided before the starting of transferring each message. Both the types of signaling and communication are applicable in different fields of application.

Comparison between Asynchronous and Synchronous:




Form of Signal required for Transmission

In one form of asynchronous transmission, there is only one wire/signal carrying the transmission.

In synchronous transmission, the stream of data to be transferred is encoded as fluctuating voltages in one wire, and a periodic pulse of voltage is put on another wire (often called the "clock" or "strobe").

Transformation of Message Methods

sender provides a synchronization signal to the receiver before starting the transfer of each message

sender and receiver use the same clock signal


  • does not need clock signal between the sender and the receiver
  • slower data transfer rate
  • supports high data transfer rate
  • needs clock signal between the sender and the receiver
  • requires master/slave configuration


  • Simple, doesn't require synchronization of both communication sides
  • Cheap, because Asynchronous transmission require less hardware
  • Set-up is faster than other transmissions, so well suited for applications where messages are generated at irregular intervals, for example data entry from the keyboard and the speed depends on different applications

Lower overhead and thus, greater throughput


Large relative overhead, a high proportion of the transmitted bits are uniquely for control purposes and thus carry no useful information

  • Slightly more complex
  • Hardware is more expensive

Communication Examples

This communication works much like the postal system

This communication works much like a phone call.

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