Whenever a traditional web application needs to update a page, it does what is called a “round trip” to the server. The entire page is sent to the server, and then a whole new page is sent back. You will often see the whole page refresh in the web browser screen. This typically happens when you click on a link or a button in the browser window. This is not a very efficient use of network bandwidth, particularly if the change is small. Depending on the speed of the network and the server the browser is communicating with, this process can also be slow. It’s reminiscent of the way old mainframe terminals used to work, except that they were completely text-based.
Where things stand now