This setting enables the semi-hosting support and configures input/output to print information to the console during debugging.
No I/O - no printing will be done.
Debugger Console - the output will be printed out to the console provided by the debugger specified in the Debugger setting.
Real-time printf with ITM - the Instrumentation Trace Macrocell (ITM) block provides a mechanism for sending data from your target to the debugger via the SWO trade stream.