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Sierra's Creative Interpreter (SCI) is the scripting language created by Jeff Stephenson of Sierra Online for its adventure games after the older AGI, and the runtime environment for such adventure games. While AGI was a procedural language, SCI is completely object-oriented.

Although ports for the Amiga, Atari ST and Macintosh platforms exist, the primary development was for the IBM PC platform.

Although continuously developed between 1988 and 1996, five major versions can be isolated.

SCI0

First used for King's Quest 4 in 1988, SCI0 (0.000.xxx) allowed for 320x200 graphics with 16 colors as well as a music-card compatible soundtrack. It also supported parser-based keyboard input which a game could be scripted to use if it wishes to do so (non-adventure games usually didn't). Later versions of SCI0 added bilingual support for international versions; their version string reads "S.OLD.xxx".

SCI1

Released in 1990, the most notable improvement in SCI1 (1.000.xxx/T.A00.xxx) was the support of 256 color graphics, still at a resolution of 320x200; EGA 16 color graphics were still available (games were usually sold in separate 16 and 256 color versions). Some people prefer to call the 16-color SCI1 interpreters "SCI01". With the shift to SCI1, Sierra began using a digitized painting process for background artwork, rather than the pixel-by-pixel process of previous engines: the difference is readily apparent if one compares, for example, King's Quest 4 against King's Quest 5.

Most SCI1 games are completely mouse-driven, using an icon-based interface; contrary to popular thought, it is up to the game's script code, not to the interpreter, to implement the user interface. For example, even though Quest for Glory 2 is parser-driven and King's Quest 5 is mouse-driven, they use compatible interpreters, as it is possible to use the interpreter from QFG2 with the EGA version of KQ5.

The version numbering scheme is somewhat confusing for the reason that the third number in the version string (the build number) has only three digits, even though four are needed. For example, the game Space Quest 4 Version 1.052 ships with an interpreter labeled "1.000.753", whereas the game Conquests of the Longbow Version 1.0 ships with an interpreter labeled "1.000.168"; nevertheless, the latter interpreter is newer because the build number is actually 1168, not 168. Also, in some cases the "1.000" is replaced with "T.A00", which however does not indicate a separate development fork.

Interpreters with build numbers >1000 have slightly modified file formats and improved foreign language support (resulting from a code merge with SCI0's S.OLD fork), but are otherwise like earlier SCI1 versions.

SCI1.1

Apart from considerable internal changes, SCI1.1 (1.001.xxx) added support for animated movie sequences (first used in KQ6) as well as scaling sprites: characters would become smaller as they walk into the distance, giving a pseudo-3D effect. (The interpreters from some early SCI1.1 games bear a "2.000.000" version stamp; this is most likely an inconsistency which should be ignored.)

Separate 16-color packages were no longer available; EGA owners instead would be presented a 640x200 graphics display that simulated 256 colors via dithering.

SCI2

Often called SCI32 (along with SCI3), SCI2 (2.xxx.xxx) runs in 32-bit mode by using the DOS/4GW extender or by running it in Windows 3.1's Enhanced Mode. Most notable is the support of high-resolution 640x480 graphics, as well as better movie support. There are two known revisions, 2.000.000, and 2.100.002.

SCI3

The last version, SCI3 (3.000.000) could not only run under DOS or Windows 3.1, but also natively under Windows 95.