/vr/ - Retro Games

>>1471948
This phenomenon is called ghosting, and arises due to how keyboards are designed.

The keyboard keys are laid out on a matrix, which is the circuit responsible for connecting the key switch to the electronics responsible for figuring out which key is pressed. Depending on how it is designed, it might not be able to read multiple keys at the same time. This is often the case because the most common use case of keyboards is typing, where only one key is actually being pressed at any given time. Care is usually taken to allow for modifier keys such as Ctrl, Alt and Shift to be pressed with anything. This significantly reduces the cost and complexity of the hardware itself, but ends up making the input device unsuitable to certain applications, such as gaming.

How many keys you can press together is called the key rollover. A keyboard with 4 key rollover lets you press 4 keys at the same time. There are keyboards that don't quite use a matrix; they scan each key switch independently, and thus support an arbitrary number of keys pressed at the same time. This is called N-key rollover, or NKRO. They are ideal for gaming. This technology is also used in devices such as piano keyboards.

See this site for an application that will help you test and determine which keys you can press together at the same time:

https://www.microsoft.com/appliedsciences/content/projects/KeyboardGhostingDemo.aspx