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Intel now sell their CPUs with an advertised Core Clock speed, and a Turbo Boost (up to) speed.

As well as this, thanks to SpeedStep (dynamic frequency scaling), a CPU will often underclock to conserve power and reduce heat. Therefore, a CPU rarely sits at its advertised core clock speed anymore; it's constantly changing in realtime between its minimum clock speed, and its Turbo Boost speed.

Take for example, my dual-core Core i7-4650U:

- Base clock: 1.7GHz
- Minimum/idle clock: 0.8GHz
- Turbo Boost (with both cores active): 2.9GHz

Here's I tried to post a graph displaying the clock speed of my CPU over the time it took to write this question (using Intel Power Gadget), but I need 10 rep to post an image, so you'll have to take my word for it: the frequency was rarely (if ever) set to 1.7GHz.

If I earn 10 rep in the meantime, I'll upload the image :)

So, my question is: what does the base clock speed of an Intel CPU actually indicate anymore? Personally, as a consumer, all I really care about is how low (for power savings) and how high (for performance) a CPU can be clocked at.

Hennes
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cathalog
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6 Answers6

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The base clock speed is a guaranteed clock speed for full typical (but not peak) utilization. As long as one is not running a power/thermal virus (i.e., not peak utilization), one should be able to fully use the hardware at the stated clock speed without violating the thermal design power.

When software is not using all the available cores, or sufficient cooling is provided, some additional thermal headroom is available which can be exploited by increasing the clock speed of the active cores (Turbo Boost).

Incidentally, minimum clock speed is not especially useful for evaluating energy efficiency since a significant amount of power consumption is static power (independent of the work done). At a certain point, race to sleep (a.k.a., hurry up and go to sleep) will be more energy efficient than reducing the clock speed because sleep states reduce the static power use.

Tag
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The Thermal Design Power (TDP) of Intel cpus is also tied to the base clock speed of the processor.
So when the processor is running at the base clock on all cores it should not exceed the TDP, but if it uses Turbo Boost the power consumption of the cpu can be much higher than its TDP.
So in use cases where the processor is tied to its TDP as the power budget for e.g. in some notebooks or some OEM machines the cpu will most likely not exceed the base clock when its load is at 100%.

Vorgartenzwerg42
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This is a really poor answer, I know,

It signifies the maximum speed of your processor.

Your CPU is only going to work as hard as it needs to, to complete the specified task.

As an example you can split in your processor frequency into 17 imaginary people. Let's say each person is equivelant to 100MHz of clock speed. If the task the people have to complete is push a button every time some water drips into the pail, and each person can push the button up to 5 times a second, releasing 1 unit of water from the pail every button push.

And if water is dripping into the pail 1 units per second, we only need 1 person pushing the button. However the minimum amount of people at work is 8 so there will be 8 people (your lowest clock of 800MHz). No need to have 17 people present wasting energy (did I forget to mention we're in space and oxygen supply is limited?) when it's possible to only have 8 people. (Compare oxygen to power usage)

But if you have water coming in at 85 units per second, you're going to need all the help you can get pushing those buttons! 85 / 5 = 17 ! 85 units per second / 5 units per second per person = 17 persons That's your entire team. (17 people = your base clock of 1700MHz) A cpu with a lower base clock than 1.7GHz would not be able to keep up with a load that large and the application would lag.

Turbo boost is more complicated to explain, and only is taken into effect when your other core doesn't have as large as a load as the core in question, or the CPU is not using much energy. But it further boosts the strength of that core when extra strength is needed.

CausingUnderflowsEverywhere
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Base clock (BCLK) speed is the speed at which the CPU communicates to the "partner" chips around it, such as the northbridge/southbridge..IDK why they still use it, but it's more of a reference or baseline system speed...We USED to increase the base clock, back in the days before unlocked processors...Wasn't very effective though.. It is sort of the "heartbeat" of the motherboard...Or rather the frequency at which the system's heart is beating...The motherboard and supporting chips are the heart, the cpu is the brain, the ram is the memory...

Now the base frequency of a CPU is it's low power state speed or totally idle speed...With my old 4790K AND my new 8700K it is 800MHZ...You'll know when you've messed up a setting in the BIOS or in Windows if your CPU is stuck at 800 mhz...Usually due to some Windows power saving mode being enabled...It is fun to sometimes make it 800 mhz and try to use windows at that speed..Makes you appreciate 4.0 Ghz and above!

Marccss
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It also is the speed a laptop cpu will try to run at full usage when on battery power my laptop can run at 4.4 Ghz when plugged in but when using the battery it will stay around 2Ghz the base speed to save power

Christopher Young
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the base for power savings is the lowest of your cpu clock speed. while the highest for high performance mode (usually playing games and heavy software) use the maximum of your clock. Sometimes, it depends on the how many task and process your system's running. The more and use a lot of resources means more clock speed.

Hadi Faizul
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