For microprocessors, the purpose is generally to decrease the need for heat dissipation devices or decrease the electrical power consumption. This can provide increased system stability in high-heat environments, or can allow a system to run with a lower airflow (and therefore quieter) cooling fan or without one at all. For example, a Pentium 4 processor clocked at 2.4 GHz can be "underclocked" to 1.8 GHz and can then be safely run with reduced fan speeds. However, this invariably comes at the expense of some system performance. "Underclocking" can also be performed on graphics card processors (GPUs), usually with the aim of reducing heat output. For instance, it is possible to set a GPU to run at lower clock rates when performing everyday tasks (e.g. internet browsing), thus allowing the card to operate at lower temperature and thus lower, quieter fan speeds. The GPU can then be overclocked for more graphically intense applications, such as games. "Underclocking" a GPU will reduce performance, but this decrease will probably not be noticeable except in graphically intensive applications.
