Introduction to Agi

In the mid 1980's, Sierra created the first '3D' graphical adventure game and was a showcase for a new computer that was being released: the IBM PC Jr. The game was King's Quest.

The game was created using a technology known as AGI, which stands for Adventure Game Interpreter. The popularity of King's Quest led to several sequels and new series to be developed using AGI.

At the time, several computer makers were competing for the personal computer market share. Apple IIe, Apple IIgs, Atari ST, Amiga, IBM PC, Tandy Color Computer 3, Tandy 1000 all had some AGI games developed for them at some point during the lifetime of AGI. The last game to use AGI was released in 1989 (Manhunter: San Francisco). After that, all Sierra adventure games used the successor to AGI, known as SCI. King's Quest IV is the only game that was released for both AGI and SCI (it was the first SCI game).

In order to ease the creation of the games, and the porting to the many different platforms that were popular at the time, Sierra needed a technology that could make them productive. Games needed to be created quickly, and ported to the different platforms without much effort.

What they chose to do is to implement the games using a custom scripting language. By packaging all of the game resources (logic scripts, animations, sounds, etc.) together, the game implementation could be separated from the game interpreter. The interpreter would provide the desired abstraction from the underlying computer platform. An interpreter would be written once for each supported computer platform, and it could be reused many times, for each game that was being developed.

This worked out so well that Sierra released 14 games that used AGI. The technology was revised slightly throughout the years, but remained essentially the same.

The successor to AGI: SCI

AGI games were a success, but hardware technology was advancing rapidly, and AGI wasn't designed to support the latest and greatest. Sierra's competition were producing games that had better graphics. A more powerful technology was needed to replace AGI. Sierra created a new system named SCI (Sierra Creative Interpreter).

The first iteration of SCI produced games that had a gameplay similar to AGI, but with higher resolution graphics. AGI was limited to 160x200, while the first version of SCI used 320x200. Games still used a (more advanced) text parser for user input. Sound cards allowing significant better sound than the PC speaker or Tandy 1000 sound chip were coming out, and SCI supported these as well.

It didn't take long for VGA cards to become standard, so the second iteration of SCI supported 256 colors. The parser interface was dropped in favor of an icon interface. In a later iteration, the resolution was increased to 640x480.

SCI was used to produce even more games than AGI. The last revision of SCI was used to produce Leisure Suit Larry 7.

Agi games

Sierra released a total of 14 AGI games, as well as a few demos.

The last AGI game to be released was Manhunter: San Francisco, in 1989. Some of these games had more sequels, but those were developed using Sierra's newer SCI technology. Some remakes of the AGI games were also developed using SCI.

King's Quest I was the first game to be remade using SCI. It featured 16 color graphics, but at a higher resolution (320x200). Mixed-Up Mother Goose was also remade in 16 colors high resolution.

Later, when SCI games switched to an icon based interface and supported 256 colors, Sierra remade Leisure Suit Larry I, Police Quest I and Space Quest I. These were sold at budget prices, but alledgedly didn't sell too well, so this was the end of remakes. Mixed-Up Mother Goose was the exception, and was remade a few more times in 256 colors.

For King's Quest IV, Sierra released both an AGI and SCI version of the game, around the same time. The memory requirements for SCI were greater than AGI (512K vs. 256K) so the users had the option of getting the version appropriate for their machine.

Many years later Sierra released collections of their adventure games on CD. These collections typically contain only the SCI version of the games, when both AGI and SCI versions exist.

Agi platforms

In the 1980's, several computer makers were competing for the personal computer market share. Apple IIe, Apple IIgs, Atari ST, Amiga, IBM PC, Tandy Color Computer 3, Tandy 1000 all had some AGI games developed for them at some point during the lifetime of AGI.