The X 86 Microprocessors: Architecture, Programming and Interfacing (8086 to Pentium) 2nd Edition by Pearson

In this, some of the DOS 21H functions and the BIOS 10H and 16H functions are listed.

i) List of important DOS INT 21H services

DOS system calls use the 21H vector. Some of the important INT 21H services are

listed here.

Function No. Action Returns/Expects

AH = 01 Read character from

standard input device with

echo

Returns:

AL = ASCII of the input key

AH = 02 Write character to

standard output device

Expects:

DL = ASCII code of output data

AH = 05 Write character to printer

Expects:

DL = ASCII of the output

AH = 08 Read character input from

standard input device,

without echo

Returns:

AL = ASCII of the input key

AH = 09 Display string

Expects:

DS:DX = segment: ...