The Demoscene is a computer art subculture that specializes in producing demos — programs that, when run, produce some form of audiovisual presentation in real-time.
Demos are typically written completely from scratch using custom code, and usually comprise a blending of artistic creation and programming techniques that push the limits of the hardware, often in ways previously thought unachievable.
Demos originally started in the 1980s as "cracktros" — custom Loading Screens created by pirate groups that managed to remove the Copy Protection from software and added their own intro to promote themselves. Over time, these intros became increasingly elaborate as crackers were keen to show off what they could do even with the extreme limitations imposed by the hardware.
Eventually, the intro aspect was dropped completely, and evolved into full demos that were released without being attached to existing software, and the Demoscene was born.
Being rooted in pirate and hacker culture, the Demoscene has a strong anarchic thread, which often influences the artistic style of demos. Unconstrained by graphical convention, Demosceners often experiment with bold and ostentatious art styles and typography. Lavish graffiti-styled logos are a common sight, as are "scrollers" — Scrolling Text which is often designed more for showcasing graphical effects than for readability.
(It should also be noted that the Demoscene is unregulated, uncensored, and has no requirement to adhere to content ratings - be aware that demos aren't always family-friendly in their language or imagery).
The Demoscene also has a strong competitive streak, as groups vie to push hardware to its absolute limit to achieve groundbreaking new effects. This was initially motivated by the fact that the hardware of the 1980s and 1990s was extremely limited by today's standards, requiring considerable coding ingenuity to get the most out of the systems.
While computing power has long since surpassed the meager limits of those early systems, the Demoscene still continues to this day, with Demosceners often accepting voluntary constraints in order to test their skills, such as extreme restrictions on demo filesizes. Writing demos for obsolete systems is still popular, with new techniques continuing to be found, and some also enjoy the challenge of creating demos for more esoteric systems such as embedded hardware. In more recent years, the rise of fantasy consoles (modern software that seeks to imitate the retro aesthetics and harsh limitations of older hardware) has also given rise to a whole new facet of the Demoscene, centered on platforms like the PICO-8 and TIC-80.
Demos are often categorized into different groups based on their size and platform. While demos certainly exist for just about any platform, the most popular are PC (meaning MS-DOS until around 1999 and mostly Windows thereafter), Amiga, Commodore 64, ZX Spectrum and Atari home computers (both 16/32-bit (Atari ST-compatible) and 8-bit (400/800-compatible)).
PC and Amiga demos are usually divided by size. There are demos which have very loose size restrictions and where the demo is only limited by the creator's imagination, then there are demos restricted by size. Size-restricted demos are usually called intros. The most common categories for size-restricted demos are 64 kilobytes and 4 kilobytes, although there are even smaller quality demos and competitions like 1-kilobyte, 256-byte, and 32 bytes or less (by which point they are typically DOS comfiles so as to dispense with executable headers). note Smaller demos usually rely heavily on procedural generation where assets such as 3D objects and textures are generated using simple algorithms.
When used as a genuine examination of how well a new system is expected to perform (for attracting interest at trade-shows and the like), such processes are typically referred to as technology demos. Technology demos are usually made by the hardware companies themselves, however, not the demoscene.
As a side-note, size-limited demoscene productions typically use obscure executable compression which, outside the demoscene, is only ever used to cloak malware. It is therefore not unusual for antivirus or antimalware software to report clean demoscene files as infected. Likewise, it can be difficult to tell if something actually is infected.