Prompting messages begin with ENTER or REENTER, and require a response from the user.

Mode messages are the READY messages sent by the terminal monitor program, and any other similar messages sent by Command Processors, such as the EDIT mode message sent by the EDIT Command Processor. They inform the user which command is in control and let the user know that the system is waiting for the user to enter a new command or subcommand.

Informational messages do not require an immediate response from the user.

Messages should usually have other messages associated with them that more fully explain the initial message. These messages, called second-level messages, are displayed only if the user specifically requests them by entering a question mark (?) in response to the initial message. Prompting messages can have any number of second-level messages. An informational message can have only one second-level message associated with it. Mode messages cannot have second-level messages.