Clock speed is all important to CPU performance.
In mobile environments performance is important but power efficiency is paramount, especially when peak performance is not required.
Many factors affect performance in all of these scenarios but one constant factor is the clock.
In the CPU the clock signal determines when things happen.
A faster clock tick rate means more operations in a given time.
This sounds great, surely you just want it to tick as fast as possible then, right?
Firstly, every tick of the clock causes a pulse of power.
This power has to come from somewhere.
It also results in the production of heat, which then must be dissipated.
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Power and thermal management
There are two main uses of electrical power.
The first is the constant current of a system that is powered on.
The second is the surge from a system being turned on.
The clock signal drives that switching.
It also, alone, contributes a non-trivial amount of that power usage.
The thing is, some pieces of hardware on a CPU arent needed in every CPU cycle.
In most clock cycles, an individual register for example, wont be needed.
By disabling the clock signal behind the gate, the main source of power usage can be removed.
This can help to significantly decrease power consumption, which is especially important for battery-powered devices.
The absolute speed limit
We mentioned before that it gets harder to synchronise fast clocks.
Unfortunately, that is a hard and fast rule imposed by basic physics.
The fastest speed at which anything can travel is the speed of light in a vacuum.
Thats roughly three hundred million meters per second (or 670,600,000 miles per hour) thats really fast.
Another thing thats really fast is the clock speed on modern CPUs.
5.7GHz or 5.7 billion ticks per second translates to one clock tick every 175 picoseconds, or 0.175 nanoseconds.
Its 55mm or 2.1 inches.
Now computers dont run on photons, at least they dont yet though photonics is an advancing field.
Computers run on electrons which move slower.
Each of these delays the signal propagation.
As mentioned, intervening electronics slow down the clock signal propagation.
This is true even for clock gates.
As such, during CPU design, its important to take this into account.
Its also important to understand exactly what effect this can have on the overall shape of the clock signal.
Conclusion
A Clock Gate is a circuit component used in processor design.
It prevents or enables the synchronising clock signal from reaching one or more further components.
This essentially acts as a switch.
It also prevents that energy from being converted into heat.
This leaves more thermal and power budget for other components of the processor that are being used.
Alternatively, it reduces the overall system load on the power and cooling system.
