King's Quest III: To Heir is Human (AGI)

Released: 1986
Published by: Sierra On-Line, Inc.
Developed by: Sierra On-Line, Inc.
Credits: Roberta Williams, Ken Williams.

VGA/MCGA is an option, but it just runs the same as EGA, with 16 colours

System Requirements

System Requirements 8088 or 8086 and compatibles. 256K RAM required. DOS 2.11 or later. Hercules monochrome/CGA/EGA/VGA graphics supported. Audio support for PC speaker or Tandy only. Supports a joystick. *An unofficial "experimental" patch allows 3-voice music to be played from an MPU-401 interface*
Original Media Three 5.25" 360 KB (DD) disks (original version 1.01 and 2.00 version), or two 3.5" 720 KB (DD) disks (version 2.14).
Installed Size 1 to 1.5 MB of hard disk space.


From where can it be run?

From the original floppy disks only.


Game Audio/Video

AGIMIDI is after patching the PC speaker driver using the AGIMIDI utility to produce 3-voice sound.
PC Speaker Intro 
Tandy 1000 (emulated) Intro 
AGIMIDI 3-voice Intro 


Copy Protection

All versions of King's Quest III (in fact all AGI2 titles from Sierra) were supplied with the first disk being a "Key" disk - an early copy protection method. Key disks used a track on the disk (usually track 0) that had a checksum error or used a non-standard sector size on that track. The main executable file (SIERRA.COM) would make a check for this non-standard track, and if found would read a decryption key from it and decrypt the real executable file, which is "AGI". This protection was called "SuperLok 3.2".


How to Setup

The game does not come with a setup program like later Sierra titles. All versions check the BIOS for an ID string that matches an IBM PCjr or Tandy 1000 and will initialise those systems' 3-voice PCG sound data and also load those graphics drivers. However, there are some command-line options to force the graphics mode. Simple run SIERRA.COM with:

  • -c Forces CGA Composite colour mode
  • -r Forces CGA RGB colour mode
  • -h Forces Hercules (HGC) mono mode for TTL monitors
  • -e Forces EGA mode
  • -v Forces MCGA/VGA mode
  • -t Forces Tandy 1000 graphics and/or sound
  • -p Forces "PC" mode (assumed to tell it you're running a PC not a PCjr or Tandy)
  • -s An unknown flag - not sure what this does

My version of this game has AGI interpreter version 2.936 (the most up-to-date interpreter released for this game), and by default it runs in EGA graphics mode. Running with the -c option worked well. -h wasn't tested as it requires a TTL (digital signal) monitor. -v I hoped would work but displayed corrupted EGA graphics.

The game doesn't require any extended memory (XMS) or expanded memory (EMS) drivers to be loaded.


Issue: Corrupted graphics or garbled text, unreadable.
Cause: This can occur if running the game with a modern graphics card under Windows 95, 98 or ME.
Resolution: Either run it on period-correct hardware (including the graphics card) or run it in DOSBox. There are also several third-party AGI interpreters that fix many bugs when running on more modern computers - try ScummVM or NAGI. There was another called Sarien but that has since merged with ScummVM.


To Quit the Game

Simply type the word "QUIT" and hit enter. Then either hit ENTER again to confirm or ESC to cancel.

Supporting Documents

Here are the original documents that came with the game:

And here are some aftermarket links:

Save Games

The location of save game files is entirely up to you! When you type the word "SAVE" you will be prompted for a directory where you wish the save game file to be stored. By default this will be the same directory in which the executable file was run.

Once you've chosen the location you are shown 12 'slots' in which save games can be stored. Any slots that have a save game already stored will display their description. Once the slot has been chosen, you are prompted to give a description for the save game. Once completed, the save game will be stored in a file called kq3sg.x where x is the slot number from 1 to 12.

This is actually a great way of storing save games, as you are not limited to 12 slots - if you need more you can create a directory anywhere and use that to store a further 12 save games.

Versions of the game known to exist

Version Date Comments
1.01 8th November 1986 5.25" 360 KB version. Comes with AGI2 intepreter v2.272. This version of the game only supports CGA, Hercules, and Tandy/PCjr graphics.
2.00 25th May 1987 5.25" 360 KB version. Comes with AGI3 interpreter v2.435. Like game version 1.01, this version only supports CGA, Hercules, and Tandy/PCjr graphics.
2.14 15th March 1988 The first version released on 3.5" floppy disks (two). It added MCGA graphics support. It came with AGI interpreter version 2.936. This makes it able to support the third-party AGIMIDI.EXE patch that allows 3-voice sound via your MPU-401 interface.