How speed and frequency of a processor are related to each other?

Question

I think that clock rate of processor determines the speed of core, in my case it is 1.86GHz. But If I am not wrong, it also determines that how much energy it will consume. If you have more frequency then more power it will consume.

I choose Power Saver scheme to increase my battery life, however it reduces my core speed to half of the actual speed. I understand this happens because of SpeedStep, but I don't see any slowdown of my computer.

So my problem is why we have such high frequency cores as it uses too much power. We can use low frequency cores.

Actually I get confused between the two terms Speed of the processor and its frequency.

So how much important is the frequency of core in case of any processor.

Answer 1

Modern CPUs run faster than the motherboards do. Thats where clock multipliers come in. If you have a 2GHz CPU and a 1 GHz bus, your clock multiplier is 2. If you have a 2Ghz CPU and a 666MHz bus your multiplier is 3.

CPUs process data faster than they can communicate. While waiting for the bus, they can and are doing work.

Higher frequency CPUs do make your computer faster, but as the CPU frequency goes up and the bus speed stays the same, the less efficient if becomes. This is because the CPU is waiting for the bus to give/take data.

So if the CPU is working while its waiting for the bus, you are using more power, but gaining little benefit.

Programs like Intel SpeedStep, lower the frequency of the CPU when not under heavy load, so it consumes less power. You might not notice a speed difference, because the lower CPU frequency might be more than capable of handling the current workload.

Answer 2

So how much important is the frequency of core in case of any processor.

Slightly oversimplifying, the perceivable speed of your CPU depends on two things: the instruction set and the clock frequency.

The former defines how many work can get done in a single cycle, the latter how many cycles get performed per second. The product is the perceivable speed.

So, if you scale down a 2 GHz processor core to 1 GHz, the perceivable speed gets cut in half.

So my problem is why we have such high frequency cores as it uses too much power. We can use low frequency cores.

For any application that isn't limited by the CPU, that's true. For example, if you copy a file from one HDD to another, the hard drives won't be able to keep up with the processor anyway, so you won't gain any benefit from a fast processor.

But CPU intensive applications (e.g., file compressors, video encoders, games) will depend on a fast CPU and become significantly slower if you don't have one.

That's why modern laptops scale the CPU frequency. When a fast CPU is not needed, the CPU runs at a slow frequency, consuming less power. When a fast CPU is needed, it runs at the highest possible frequency, making your computer more responsive.

Answer 3

In this case, clock speed and frequency are synonymous. As to why we have such high frequency cores, your computer use may only require a low clock speed, but many applications require a much higher clock speed. You really can't generalize one person's experience across all computer users.