Overview
Instant messaging requires an instant messaging client that connects to an instant messaging service. Instant messaging differs from e-mail in that conversations happen in real-time. A multiprotocol instant messaging application allows one client to connect to multiple IM networks.

Instant messaging services owe many ideas to an older and still popular online chat medium known as Internet Relay Chat (IRC). In early instant messaging programs, each letter appeared as it was typed, and when letters were deleted to correct typos this was also seen in real time. This made it more like a telephone conversation than exchanging letters. In modern instant messaging programs, the other party in the conversation generally only sees each line of text right after a new line is started. Most instant messaging applications also include the ability to set a status message, roughly analogous to the message on a telephone answering machine. 
 
In early instant messaging programs each character appeared as it was typed. The UNIX "talk" command shown in these screenshots was popular in the 1980s and early 1990s.

Benefits
Instant messaging offers real-time communication and allows easy collaboration, which might be considered more akin to genuine conversation than email's "letter" format. In contrast to e-mail, the parties know whether the peer is available. Most systems allow the user to set an online status or away message so peers are notified when the user is available, busy, or away from the computer. On the other hand, people are not forced to reply immediately to incoming messages. For this reason, some people consider communication via instant messaging to be less intrusive than communication via phone. However, not all popular systems allow the sending of messages to people not currently logged on (offline messages), thus removing much of the difference between IM and email.

Allowing for instantaneous communication between a number of parties at the same time, instant messaging can thus transmit information quickly and efficiently, as well as receive an immediate acknowledgement or reply. With the benefit of being able to see the other party using webcams, and even talking directly for free over the internet, this form of digital communication has been widely accepted by individuals of all ages.

It is possible to save a conversation, so as to refer to it later. Also, the fact that instant messages typically are logged in a local message history closes the gap to the persistent nature of e-mails and facilitates quick exchange of information such as URLs or document snippets (which can be unwieldy when communicated via telephone).