System Configuration : I/O Setup : I/O Setup Options : Sessions Overwrite Current I/O Setup When Opened

Sessions Overwrite Current I/O Setup When Opened
This option determines whether or not, when opening a session, Input, Output, and Insert I/O settings as currently configured on your system will be overwritten by any of these I/O Settings stored with a session.
*
Enable the Sessions Overwrite Current I/O Setup When Opened option for legacy Pro Tools behavior (versions lower than 8.1). This option is enabled by default.
*   
When the Sessions Overwrite Current I/O Setup When Opened option is disabled, Pro Tools recalls these settings from the system. Choose this option when exchanging sessions among different systems running Pro Tools 8.1 or higher (see Session Interchange).
*   
When the Sessions Overwrite Current I/O Setup When Opened option is enabled (default), Pro Tools recalls these settings from the session rather than the system. Choose this option when exchanging sessions with systems running Pro Tools 8.0.x and lower (see Session Interchange).
*
Enabling or disabling this option in any page of the I/O Setups affects all of the other pages as well.