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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, 2013 at 11:03

4 Answers 4

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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, 2013 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.) Aug 23, 2013 at 9:02
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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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Modern CPUs reduce the clock speed automatically when idle. This is normally a good thing and works completely transparently to the user, e.g., Intel Speedstep technology. On the other hand, some CPUs can even go beyond their maximum speed, when they are not too hot, e.g., Intel TurboBoost. Note other CPU manufacturers have similar technology.

This way the user gets maximum CPU power at minimum power consumption.

It turns out that sometimes these technologies don't work as intended. I face that problem frequently with a program called Squid. The CPU usage when drawing in Squid on my Surface is low, which implies a low MHz speed of my CPU. As a consequence everything feels slow and there is noticeable lag when drawing.

Under Linux you can set the speed of a CPU core as "root user" with

echo  800000 > /sys/devices/system/cpu/cpuXX/cpufreq/scaling_min_freq
echo 1000000 > /sys/devices/system/cpu/cpuXX/cpufreq/scaling_max_freq

where XX is your CPU core, e.g., 0 for first core. 800000 is equivalent to 0.8 GHz, which is the minimum speed of my CPU. These commands would limit the CPU to operate only between 0.8 GHz and 1 GHz, which can be useful on a laptop to extend battery life. Setting the minimum and maximum scaling frequency to your maximum CPU speed would let run your computer at maximum speed.

Under Windows RM clock was the last program I used that permitted easy CPU speed manipulation. That program only worked with CPUs up to Pentium M/AMD Athlon. If anyone know of programs that allow easy clock manipulation, please add in the comment section.

Under Windows there is one option in the "Power Options" that permits manipulating the CPU speed, called "Minimum processor state" and "Maximum processor state". You may need to enable those settings by manipulating the Windows registry. So use at your own risk.

This article Power Options - Add or Remove "Min/Max processor state" describes how to enable and disable the settings.

So, for working with Squid, I set the minimum processor state to 70% and maximum to 99%. The reason to use 70% is that I don't want the CPU to run all the time in TurboBoost mode. When I need long battery life for my Surface I have a another power profile with minimum processor state set to 5% and maximum to 30%. The downside with the way Microsoft implements the manipulation of CPU speed is that it is not possible to have your CPU run at 100% workload with a clock speed of 1 GHz. Instead Microsoft power options will throttle clock speed AND the maximum amount of CPU time used at reduced clock speed. This is the difference to the way CPU speed can be reduced/increased under Linux as just mentioned.

E.g. if you set a processor state of 50% and the CPU runs only at 1.6 GHz of a 3.2 GHz CPU then you are actually only using 50% CPU time of a CPU that is running at 50% maximum CPU speed, hence you are using 25% CPU power compared to a CPU running 100% at 3.2 GHz speed. This is something to keep in mind, since low % values can make your computer really slower.

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I use System Mechanic by iolo software. I was trying to resolve an issue with my computer not waking up from the sleep state. As I reviewed the power plans, I noticed that System Mechanic provides one which runs your cpu (all cores) at their maximum rated speed. When I switched to this plan, I noticed a definite difference in the speed of my system overall.

The computer not waking up was the result of an incompatibility with one of the removable drives I had plugged in. It would keep the computer from waking up. Once I removed it - problem solved. Discovering the power plan and then switching to it was a bonus.

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