Quiet computers are those that make little or no normal operating noise, incidentally or by design. Most desktop computers emit a constant whir, and sometimes roar of noise, from fans as they spin, disk drives (hard, CD/DVD) as they spin and read and store data, and from electrical transformers as they hum and whine. Sound is also emitted by speakers, but this is intentional, and usually considered desirable by users, if not by coworkers. Many users find computer noises distracting, even irritating, more so as they increasingly listen to music and videos on computers, and use IP telephony. Ergonomic (human factors) research in noise pollution, usually in the workplace, shows that noise harms user concentration and productivity, more so where many computers operate in confined spaces, more so where no effort is made to improve acoustics. The market for quieter computers is growing worldwide, more in Europe.