A message box is a short-lived window, similar to a dialog box, which is used to display a message to the user and to receive acknowledgement and a simple decision from the user. A message box is used to inform the user of an event in situations where the information to be conveyed is relatively simple, and the response returned by the user is limited to a single choice from a finite set of options. In such a case, the range of facilities provided by a dialog box is not required. Message boxes and their uses are discussed in detail in OS/2 Version 2.0 - Volume 4: Application Development. An example of a message box is given in Figure "Presentation Manager Message Box".
A message box displays an application-supplied text string, along with one or more push buttons such as "OK", "Cancel", "Help", etc. The user selects one of these buttons in response to the text displayed in the message box.
As defined in the IBM Systems Application Architecture CUA Advanced Guide to User Interface Design, a message box is a modal dialog with the user, since the user is required to acknowledge and act upon the message before continuing interaction. Presentation Manager allows both application-modal messages, which prohibit the user from interacting with any other window in the same application before responding to the message, and system-modal messages, which block interaction with any other window in the system until the message has been acknowledged.