Instant Messaging
Instant messaging requires the use of a client program that hooks up an instant messaging service and differs from e-mail in that conversations are then able to happen in realtime. Most services offer a presence information feature, indicating whether people on one's list of contacts are currently online and available to chat. This may be called a contact list. 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.
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.
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 viatelephone).
