http://www.personal.ecu.edu/weaverch/writtencommunication.gif
The link above, Demarcation of Online Written Communication, is designed to assist faculty in the choice of written communication they would want to employ in their course.
The written communication tools are placed on the matrix in two dimensions. Vertical placement characterizes the interaction of the tool. For instance, instant messaging is located at the top of the matrix, indicating that the participants are actively communicating.
The sharing tool is found at the bottom of the matrix, indicating that the communication is not active, meaning that information is provided, but not in an interactive way. A sharing tool could be a list of links, pictures or information.
Do not make the mistake of confusing "with" as synchronous, or "to" as asynchronous. "To" and "with" are indications of interactivity only.
Horizontal placement indicates the level of knowledge as it pertains to Blooms Taxonomy. As you look from left to right, the understanding of knowledge increases.
In the upper left corner is instant messaging. IM, as it is commonly called, is a medium that is seen as a quick way to talk with others online. This mode of written communication is for the exchange of knowledge, "When is the test?" or "Did you know that Mary is going out with Joe?"
In the lower right hand corner is article. Articles are forms of communication that are carefully researched and written documents that take the reader from inception to completion of the topic. Arguments are made and supported, and the process of synthesis is used to make an evaluation.
The placement of the communication tools is purely the opinion of the author, and your opinion might be different.