What Is the Difference between Synchronous and Asynchronous?

Answer
The difference between Asynchronous and Synchronous is that Synchronous is the more efficient method of PC communication. However Asynchronous is the most
common method of communication used for email applications, internet access and networking. Synchronous is usually used for transmission of large data bocks.

---------------------
Asynchronous communication works much like the postal system: An application creates a message (that's a piece of data such as the text String "Order 1000 barrels
crude oil", or an XML expression), and labels the message with a destination address (that's typically the logical name of a "mail box", and not an IP address).
The message is passed to the messaging middleware system.
Now the sender application proceeds happily, without needing to wait for the message to be delivered.
Synchronous communication works much like a phone call. The Receiver (callee) must be available, otherwise the conversation cannot occur.
There are many pros and cons about both models, and many details (message priorities, message persistency, forwarding and routing, etc.).
------------------------------

Advantages and disadvantages

	Advantages	Disadvantages
Asynchronous transmission	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.	Large relative overhead, a high proportion of the transmitted bits are uniquely for control purposes and thus carry no useful information
Synchronous transmission	Lower overhead and thus, greater throughput	Slightly more complex Hardware is more expensive