Page "Central processing unit" Paragraph 37

However, architectural improvements alone do not solve all of the drawbacks of globally synchronous CPUs.

For example, a clock signal is subject to the delays of any other electrical signal.

Higher clock rates in increasingly complex CPUs make it more difficult to keep the clock signal in phase ( synchronized ) throughout the entire unit.

This has led many modern CPUs to require multiple identical clock signals to be provided to avoid delaying a single signal significantly enough to cause the CPU to malfunction.

Another major issue as clock rates increase dramatically is the amount of heat that is dissipated by the CPU.

The constantly changing clock causes many components to switch regardless of whether they are being used at that time.

In general, a component that is switching uses more energy than an element in a static state.

Therefore, as clock rate increases, so does heat dissipation, causing the CPU to require more effective cooling solutions.