Our tests also revealed why Pentium 4 processors sometimes work slower than expected. Even when the CPU is not overclocked, it still can suffer from overheating because of an ineffective cooler, small system case without system fans and/or too many "hot" expansion cards, or simply because of high air temperature in the room. Whatever the overheating cause is, Thermal Control Circuit will set the performance-to-temperature ratio. And our tests showed that even a little core temperature increase from 72 to 75oC might result in a 10% performance drop by Pentium 4 3.06GHz.