INT 21h / AH=1 - read Character from standard input, with echo, result is stored in AL. INT  21h Service no. 01h Description Example MOV AH, 1 INT 21h read Character from standard input, with echo, result is stored in AL. if there is no Character in the keyboard buffer, the function waits until any key is pressed INT 21h / AH=2 - write Character to standard output. INT  21h Service no. 02h Description Example MOV AH, 2 MOV DH, 'a' INT 21h Write Character to standard output. entry: DH = Character to write, after executionAL = DH. INT 21h / AH=5 - output Character to printer. INT  21h Service no. 05h Description Example MOV AH, 5 MOV DH, 'a' INT 21h output Character to printer. entry: DH = Character to print, after execution AL = DH. INT 21h / AH=6 - Direct console input or output. INT  21h Service no. 06h Description Example MOV AH, 6 MOV DH, 'a' INT 21h; output Character. MOV AH, 6 MOV DH, 255 INT 21h; get Character from keyboard buffer (if