*The basic mechanism behind the holodeck is the omni-directional holo diode (OHO), a microminiature device that can project full-color stereoscopic images and forcefields in three dimensions. The walls of a Holodeck are covered with millions of OHDs, under dedicated high-speed computer control. OHDs manipulate tiny and subtle forcefields, allowing an individual to "feel" projected objects that are not really there. Other (inanimate) objects can be physically created by replicator matter conversion. Shaped forcefields and background imagery allow a visitor to experience volumes and distances apparently larger than the Holodeck room could physically accommodate. Forcefields create a "treadmill" effect, so a user could walk or run over seemingly great distances while the projected scenery scrolls by. *Source: Back of card