Gamers are likely to be fans of the SideWinder X4 keyboard for its anti-ghosting technology. "Ghosting is the problem that some keyboard keys don't work when multiple keys are pressed simultaneously. The key presses that don't show up on the computer or seem to have disappeared are said to have been "ghosted". On most keyboards, even some that are explicitly marketed as "Anti-Ghosting," this happens with many three key combinations. Imagine playing your favorite video game and not being able to, say, run diagonally and fire your weapon at the same time (say pressing a, w, and g simultaneously). This is a result of the internal design of most existing keyboards."
Ghosting happens when the circuitry of the keyboard isn't able to accurately signal which keys have been pressed at the same time. It's usually a result of the layout of the underlying circuitry, a grid of contact wires; press one key and it's clear which contacts are brought together, but some different combinations of multiple keys may trigger the same contact patterns. Microsoft's Applied Sciences Group explains this with an illustrations and using the app below, you can see for yourself what combinations befuddle your own keyboard:
Some keyboards marketed as "anti-ghosting" have addressed the issue for specific key combinations that are most likely to occur, but not for the whole keyboard. The SideWinder X4 solves the problem by using a resistive multi-touch technology, adding a screen printed resistor in series with each key's switch; this enables the keyboard's circuitry to read the switch states as well as the grid pattern of contacts when multiple keys are pressed. It's an inexpensive solution that doesn't require a lot of additional circuitry, which means standard manufacturing techniques can produce the more accurate keyboard.