Pushing More Than 3 Buttons On A Keyboard Causes Sound

by on November 8, 2007

Q: I can’t push more than 3 buttons at once on my computer’s keyboard. When I push 4 buttons at the same time, my computer starts making a sound. Please help me.

A: Computer keyboards use something called rollover to determine which keys are being pressed at any given time. Read the Buying considerations section of Wikipedia’s article on computer keyboards for additional information. From your question, I have determined that you are probably using a keyboard with “3-key rollover”. As I understand it, keys on a 3-key rollover keyboard compete for a limited amount of circuitry. Thus the circuitry in such a keyboard is only capable of recognizing a limited number of keys being pressed at the same time. Possible consequences of using a 3-key rollover keyboard include:

  1. You press 4 or more keys but your computer fails to recognize your input. This may be accompanied by a sound from your computer, which signifies an error.
  2. You press 4 keys but your computer correctly registers only 3 of them; the last key is recognized incorrectly.
  3. You only press 3 keys but your computer thinks that you have pressed 4 of them. My research indicates that this phenomenon is called “phantom key blocking”
  4. Some 3-key rollover keyboards have been designed to work with key combinations often used in office software such as word processors. This can result in the key combinations of games working incorrectly.

You can solve the problem you are encountering in a number of ways:

  1. Purchase a keyboard that supports “n-key rollover”. Keyboards with n-key rollover provide each key on a computer keyboard with its own circuits. Thus, the keyboard could in theory recognize each individual key even if all of them were being pressed at the same moment. This does not appear to be a feature that is often advertised by computer keyboard manufactures. You should select several keyboards that you like and then contact the maker of each for more information.
  2. Some gaming keyboards have programmable keys, which can replace complex key combinations.
  3. Select different key combinations within the games that are malfunctioning. Most games will allow you to make such modifications from an options menu.

My advice is to find a true n-key rollover keyboard. I would personally find that much easier than programming buttons on a gaming keyboard or modifying the options in lots of games. Even expensive keyboards are often 3-key rollovers — so be careful.