Intel® processors are validated and supported only when they are operated at their factory rated settings. Operating a processor faster than it was designed (overclocking) can cause permanent damage to the processor, and possibly other system components including the motherboard. Other negative results are possible including the inability to boot or calculation errors. Operating a processor outside of specification will likely shorten the life of the processor, and can also void any available processor warranty.
Although not supported, it is possible to operate a processor below its rated speed. Microprocessor operation is specified down to 1/2 the maximum rated frequency. This may be necessary for troubleshooting, or because of a motherboard limitations.