Demos are pieces of software which demonstrate a computer's audiovisual capabilities and its processing power. What distinguishes them from today's common multimedia software - e.g. Autodesk 3D movies - is the fact that most action on screen is calculated in realtime. This results in somewhat small file sizes! Computers are often used to display 3D landscapes (take a look at weather charts on TV!). Many people do this by recording digital movies. The movies are precalculated using giant computer systems and, later on, you just have to replay these movies from your harddisk. Of course, you really need a lot of disk space to store movies like that ("a lot" means several megabytes up to some gigabytes here!). The point is: demo people do it in a few kilobytes using e.g. a displaying technique called voxelspace. They don't need huge amounts of disk memory. They do it the tricky way. You see: demos are realtime multimedia.
Very often demos are embellished with artful, handdrawn computer graphics and high-quality soundtracks. Even these components fit into just a few hundred kilobytes due to carefully chosen programming methods and state-of-the-art compression techniques. For example, demo soundtracks aren't stored as ordinary raw sampled data (like e.g. WAVE-files). It's more convenient to use so-called tracker modules, which means that you just have to store each used instrument once and define exactly when it has to be played; raw samples store every instrument as often as it is played. There are tracker modules lasting half an hour and needing only 100K of disk space! As raw sampled data, they'd cover 70 megabytes, and even as highly-compressed layer-3 AudioMPEGs, they would still have several megabytes!
As creating demos is enormously time-consuming, demo authors join together in demo groups. Today, demo authors have to specialise: coders take care of programming aspects, graphic artist create graphics, and musicians compose musics. Advanced demo groups often have spezialised designer focusing purely
on design, or a press officer whose job is to promote the group's products and to keep in touch with the media.
Many demo authors are of excellent education. They feel belonging to a new avantgarde, one which combines modern computer technology with artistic claims. There are even some scientists straining to find a comprehensive theory of demo writing.
Demo scening has turned out to be a huge non-commercial entertainment industry. Each time a new demo is to be released, demo freaks all over the world get upset and try to get hold of it. Demo-related web sites get thousands of visits every day, and even companies like e.g. IBM regularly support demo parties.
Quite similar to modern fairs, demo parties offer the possibility to meet the experts and to see their latest productions. Various competitions encourage artists to create new demos, musics, graphics, intros, animations etc., the visitors have to select the finest works. Besides that, demo parties are the only places where one can find guys discussing the use of illegal commands on computer systems which perished decades ago, people surviving four days and several strange-looking pizzas without sleeping at all, and specialists that comment a faint melody with "Katakis, fifth level - I know it by heart!".