In the 20th century most computers used single-core processors and not multi-core processors. Multi-core solutions were only used in unusual cases. The usual way to make a computer faster was to increase the clock rate. But at a frequency about 4 GHz the CPU would get too hot and take a lot of electricity. This was the point when multi-core processors became more important. Therefore, the demand for multi-core processors increased. In the second half of 2006 the best processors were dual-core processors. Since 2006 the development has gone on, so that the new processors get four, eight, or more independent microprocessors. Today, single-core processors are not used in new personal computers, but they remain popular in embedded systems which do not need a fast processor.