DCAS (sometimes called ASDC) is an alternate set of movement controls to the popular WASD arrangement.
Key bind differences from WASD:
- D = forward
- C = back
- A = move left
- S = move right
- alt/cmd = crouch (when applicable)
When Bungie's first-person shooter Marathon was released in 1994, it featured up/down look control and the option to fully control turning and aiming by mouse (a feature popularized by id's Quake in 1996 as "mouselook"). However, Marathon 1 did not include a set of default controls to handle this. With WASD not yet a well-known standard, some gamers devised their own control schemes to handle combined keyboard movement with mouse aiming; DCAS was one such control scheme.
Initially, the DCAS style in Marathon was used with the caps lock key bound to run; however, this violated the "oath of the vidmaster", so a similar style FVAS was devised to keep the D key available as an easy-to-reach run key. Later, using shift for run with the DCAS keys was considered a better solution.
Like WASD, DCAS allows the player to easily utilize the left modifier keys; this is advantageous because on most keyboards, the circuitry is better at tracking multiple key-presses simultaneously if some of them are modifier keys. Configurations that move the hand towards the center of the keyboard (like ESDF and RDFG) make the modifier keys harder to reach.
Unlike WASD, the position of the left hand for DCAS gaming is very similar to the left hand's position on the home row keys. This is very comfortable for right-handed gamers and is seen as the primary advantage over using WASD, though it is ill-suited for left-handed mousing.