Hello World in simple assembly language

DATA SEGMENT
    STRING DB 'Hello World!','$'
DATA ENDS

CODE SEGMENT
    ASSUME CS:CODE, DS:DATA
START:
    MOV AX,DATA
    MOV DS,AX
    MOV DX,OFFSET STRING
    MOV AH,09H
    INT 21H
CODE ENDS
END START

AH	Features	Entry parameters	Export parameters
4CH	Return to DOS	no	no
1	Enter a character into AL by keyboard	no	AL = Character
2	Output the characters of the DL register to the display	DL	(Store one character)
9	Output a character string ending in "$" to the display	DS: Segment address where the string is located DX: String first address	no
0AH	Enter a string from the keyboard to the specified buffer	DS: segment address where the buffer is located	DX: buffer first address