Sierra Creative Interpreter

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The Sierra Creative Interpreter (SCI) was a game engine developed by Sierra On-Line in the late 1980s as a successor to the earlier AGI (Adventure Game Interpreter) engine. SCI first appeared with King’s Quest IV in 1988 and powered many of Sierra’s adventure games through the 1990s. It introduced higher-resolution graphics, a point-and-click interface, a more sophisticated scripting language, and support for richer audio and animation.^[1][2]

Sierra realized AGI (originally developed for the IBM PCjr) was “under-equipped” for the new multimedia era.^[3]

To meet this challenge, Sierra engineer Jeff Stephenson proposed a completely new, object-oriented interpreter.^[4] As he recalls, “AGI was written in such a way that it was going to take a major rework of the entire game engine…and so that’s when I pitched Ken on SCI…let’s go with a whole new language, we’re going to have to rewrite this thing anyway, let’s make things better.”^[5]

The result was SCI (initially called LSCI for Large-model Script Code Interpreter), a virtual “bytecode” engine that could be compiled for any platform.^[3] As Roberta Williams explained, SCI was designed as “a virtual machine language which means that it will work on any machine…Each machine format has its own version of SCI. Our games are never IBM conversions.”^[6]

SCI’s design drew on then-modern programming ideas. Stephenson was influenced by Object-Oriented languages like Smalltalk, which he discovered in a 1981 BYTE issue.^[5] He rewrote Sierra’s scripting language into a more structured, object-oriented form. As one retrospective notes, “Stephenson completely rewrote the language…going from a simplistically cryptic scripting language to a full-fledged modern programming language reminiscent of C++, incorporating all the latest thinking about object-oriented coding.”^[7] In practical terms, SCI scripts could define classes for rooms, actors, puzzles, etc., making the engine more flexible.

King’s Quest IV (1988) was the first title to employ Sierra’s Creative Interpreter engine, demonstrating the engine’s expanded multimedia support.^[8] It featured a full orchestral score by William Goldstein, one of the earliest uses of a Hollywood-style soundtrack in a computer game. These audio enhancements illustrated SCI’s ability to handle more complex musical arrangements and contributed to a more cinematic adventure experience.^[7]

SCI was developed in successive versions, each offering technical advancements:

SCI was an interpreted engine using a proprietary scripting language with object-oriented features. It supported platforms including MS-DOS, Windows, Macintosh, Amiga, and FM Towns. Graphics support ranged from 16-color EGA in SCI0 to 256-color SVGA in SCI2/SCI3. SCI also supported a variety of sound hardware, including AdLib, Sound Blaster, and Roland MT-32.^[15]

• King’s Quest IV-VII
• Space Quest III-VI
• Leisure Suit Larry II-VII
• Police Quest II-IV
• Quest for Glory I-IV
• Gabriel Knight I-II
• Phantasmagoria I-II
• Freddy Pharkas: Frontier Pharmacist
• EcoQuest I-II

SCI was one of the leading adventure game engines of its time, alongside LucasArts' SCUMM. It influenced modern engines like Adventure Game Studio. Preservation efforts include support for SCI games in ScummVM, which merged with the FreeSCI project in 2009.^[16]

• Interview with SCI engineer Jeff Stephenson on YouTube