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In regards to my CPU, most article (include the Wiki) told me that I must use "FSB", but I don't have such a value (see below) so I have some question about CPU:

Intel(R) Core(TM) i5-4670 CPU @ 3.40GHz

What does the "3.40GHz" mean?

Clocks (Core #0)
Core Speed : 801.4MHz <-1.4MHz more than Intel published
Multiplier : x36.0 <-changing continuous, but most cases lower than 40
Bus Speed : (empty)
Rated FSB (<-graytext) : (empty)

How to understanding these values? Can I do something like 801.4*36/1000? I notice that windows8 taskmgr shown my CPU speed is "0.80GHz"

But some time later, it suddenly jump to 1.60GHz and back to 0.8 in few seconds Is my computer run in power saving mode? Or my CPU support something like turbo mode?

PS: CPU temperature always low enough (About 40°~60°).

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Your CPU isn't unlocked so you don't be able to modify the FSB value. Your CPU has the ability to overclock and underclock itself. –  Ramhound Aug 23 '13 at 11:03

2 Answers 2

up vote 2 down vote accepted

What does the "3.40GHz" mean?

Nothing, it's just a text string put in the CPU by the manufacturer. Your CPU's name is "Intel(R) Core(TM) i5-4670 CPU @ 3.40GHz". Intel generally puts the "advertised" speed (the highest speed all cores can run at all the time under typical cooling conditions and default settings) there.

Is my computer run in power saving mode? Or my CPU support something like turbo mode?

The core speed drops when the CPU is not under load to keep the CPU cooler. These CPUs do have a turbo mode that is limited by temperature, so keeping the CPU cool when it's not under load helps to leave more room for upping the clock when it is under load. Your CPU can turbo up to 3.8GHz at default settings.

Intel CPUs haven't had an FSB in a long time. All Core i3/i5/i7 CPUs have an integrated memory controller.

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dose 40 * 800/1000=32 have any meaning?(CoreSpeed *Multiplier) –  GongT Aug 23 '13 at 7:47
    
Divide by 8. 800/8*40 = 4GHz. (4 because the bus is quad-pumped and two because the clock signal has two edges.) –  David Schwartz Aug 23 '13 at 9:02
    
thanks! exactly what I need! –  GongT Aug 25 '13 at 15:26

Your CPU supports both Turbo Boost and SpeedStep.

This means it can lower/increase its clock speed from 3.4GHz depending on how much load it is given. The higher the clock speed the better the performance, but power consumption and temperature are also increased. As it is a quad-core processor it also has the ability to temporarily deactivate cores in order to allow the other ones to run faster without exceeding the power/temperature limits.

According to Intel the maximum clock speed via Turbo Boost is about 3.8GHz. However, this is likely only possible with just one of the four CPU cores active.

The changes in clock speed will partly be influenced by the Power Options settings in Windows. If you set the current power plan to High Performance the CPU will tend to stay at a higher clock speed all the time, where as choosing Power Saver will make the CPU prefer lower power states.

To get a better idea of how the CPU is behaving, try downloading CPU-Z which is a very popular CPU monitoring tool:

CPU-Z

Sadly I am stil running a Core 2 in this particular machine which is not the best example but it does still have some limited frequency scaling functionality.

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