Asynchronous serial data transfer

In most computer asynchronous mode of data transfer is used in which two component have a different clock. Data transfer can occur between data in two ways serial and parallel. In case of parallel multiple lines are used to send a single bit whereas in serial transfer each bit is send one at a time. To tell other devices when the character/data will be given a concept of start and end bit is used. A start bit is denoted by 0 and stop bit is detected when line return to 1-state at least one time, here 1-state means that there is no data transfer is occurring. 

When a character is not being sent then line is kept in state 1. Start of character is detected when a 0 is sent. The character bit always come after 0 bit. After last bit is sent the state of line to become 1. 

The diagram below shows this concept:

Here earlier state of line was 1 when a character has to be send a 0 is send and character bit are transferred. 

Difference between serial and parallel transfer –

Serial	Parallel
Require single line to send data	Require multiple line
Less error and simple model	Error prone and complex working
Economical	Expensive
Slower data transfer	Faster data transfer
Used for long distance	used for short distance
Example:Computer to Computer	Example:Computer to Printer