What is it?
Well, take, in comparison, this website. It consists of a number of elements:
That about sums it up, or have I forgotten anything? Point one and four are contained within the pages themselves; point three partly within the pages, and partly in seperate stylesheets, while the images are seperate files. These are all just data, they don't do anything by themselves.
To bring this website alive, you need a browser. It may be Opera on Windows, Konqueror on Linux, Mozilla on FreeBSD, Internet Explorer on OS 9 or Safari on OS X, or some browser or operating system I never even heard of. I don't know. I don't care. I supplied the data according to well-defined specifications, and any browser on any operating system should work.
Actually, a game isn't all that different.
The elements, of course, are a bit different. There will be the media: graphics, sounds, music. There will be maps or rooms, depending on the type of game, and there might be a database, if lots of number crunching is involved. All these are passive data, and if the developers choose to do so, can be cleanly seperated from the executable that gets all this to work.
This clean seperation is often additional work, but has its advantages for the developers. They can far more easily port their game to another platform, or create a new game based on the same engine.
LucasArts were among the developers that performed this clean seperation. Their engine is known as SCUMM, which is an acronym for Script Creation Utility for Maniac Mansion. Maniac Mansion was the first game this engine was used in. Others are Loom, the Indiana Jones adventures, Sam & Max and many more.
ScummVM is nothing but a re-creation of this engine, designed to run on a wide variety of contemporary platforms. Additionally, it will run a number of games by other developers, especially by Revolution Games, for example Beneath a Steel Sky. So, if you happen to own one of these games, you can now play it on platforms that didn't even exist when it first came out. Mind that regardless of what platform you want to run it on now, it usually works best if you have the PC (DOS) version of the game.
