The following table summarizes the main I/O functions. These functions are used to read a character or a string from the keyboard and display it on the screen. They are used to input data to a program, and display characters or strings, which could be the output of the program.

FunctionInput in Effect
01H AH Read a character with echo on the screen and store it in AL.
02H AH,Character in DL Display the character given in DL on the screen. AL=Character Displayed.
06H AH,Character in DL Same as function 02 but interrupted by Ctrl + Break.
08h AH Read a character without echo and store it in AL.
09H AH, offset in DX Display the string terminated by a ‘$’ sign, starting at the address given in DX.
0AH AH, offset in DX Read a string of characters from the keyboard and store it at the address given in DX.

Table: Simple I/O DOS function calls