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I installed CPUID CPU-Z in my laptop to review the features of my processor. In Windows XP it shows me the right core speed,

Clock speed- 133MHz  
Multiplier- 14  
Core speed = 133*14
           =1862MHz

This is my actual core speed. But in Windows 7 it does not show the right speed

Clock speed- 133MHz  
Multiplier- 6 
Core speed = 133*6
           =798MHz

Another strange fact is that whenever I open another heavy program the multiplier suddenly increases showing actual core speed.

Does anybody have idea about that why two different multiplier is shown in two different cases resulting in two different core speed.

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3 Answers

up vote 4 down vote accepted

In short, this is not a fault, this is a power saving feature of modern processors. Intel calls it Speedstep, AMD call it PowerNow!.

Basically when your processor is not working particularly hard it will "clock down" (or underclock if you prefer) itself in order to save power and produce less heat. When you need it to work hard it then returns to full speed as necessary. This transition is near instantaneous and if it is doing its job properly you should not really notice your system being "slow" due to the low clock speed or transitions between speed.

Newer Intel (i3, i5, i7) and AMD processors now have an extension to this whereby the processor can actually self-overclock if it is safe to do so within thermal or power limits. Intel's version of this is Turbo Boost. The idea behind this is that power is saved by keeping the processor at a higher clock rate but for a shorter time before returning to idle, the more time spent at idle the better the power savings.

The reason you might not be seeing this in XP is possibly because it requires support from the operation system and chip set drivers, if you have old drivers or have not enabled a power plan that attempts to save power then you will not see the CPU underclocking, the "desktop" or "performance" (I can't remember the name) power profile does not all CPU enable power saving features if I remember correctly.

Windows 7 enables this power saving mode by default as the delay for speed switching is imperceptible, Windows XP may need you to change to a "mobile" power profile in order to see the CPU frequency change.

As per the Wikipedia page for SpeedStep which confirms that you may need to change the power profile in order to enable CPU SpeedStep to underclock the processor:

Under Microsoft Windows XP, SpeedStep support is built into the power management console under the control panel. In Windows XP a user can regulate processor speed indirectly by changing power schemes. The "Home/Office Desk" setting disables SpeedStep, the "Portable/Laptop" power scheme enables SpeedStep, and the "Max Battery" uses SpeedStep to slow the processor to minimal power levels as the battery weakens. The SpeedStep settings for power schemes, either built-in or custom, cannot be modified from the control panel's GUI, but can be modified using the POWERCFG.EXE command-line utility.

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the turboboost is unlikely to be the case because it is a laptop computer. furthermore, noting the spike in speed relative to usage also indicates that it is a stepping issue. –  chacham15 Aug 16 '12 at 6:55
    
this might be the reason because whenever I do any heavy work the speed automatically increases. –  Deb Aug 16 '12 at 7:05
    
one other question is, can we call it underclocking? –  Deb Aug 16 '12 at 7:11
    
@chacham15 laptop processors also feature Turbo boost –  Sathya Aug 16 '12 at 7:19
1  
@Deb Underclocking is a reasonably good term for what is going on. There is also a bit more happening under the hood as the CPU can also reduce various working voltages to save power as well. –  Mokubai Aug 16 '12 at 7:57
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Let me preface this with a warning that I am just guessing as it is hard to make a determination without further information.

The likely case is that you have a cpu which can step, meaning change its speed to save power depending on usage. I am guessing that this is the case because it is typically more prevalent in laptop type environments. My guess as to why XP is different than 7 is one of two things: either the power settings are different (there is an option to optimize for power or performance) or XP doesnt support the stepping mechanism (via drivers) thereby pinning it to the max.

For completeness, newer cpus (typically desktop) have turbo-boost which allows a single core to go faster if you turn off other cores. The trade-off here is done for heat dissipation rather than power consumption (even though the two are related).

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Well the official Microsoft website claims that it's operating system has bugs while evaluating processor speed ,it states the following

The System tool of your Control Panel may not report your computer's processor speed correctly.

It occurs due to the internal formula error of the operating system

and the solution for your problem is

Check your processor speed at bios which may list out it proper speed normally third party tools used to calculate or just obtain the data from the bios settings

you can compare the processor speed in task-manager-->performance tab and in my computer properties tab

you can see the difference there and at last the difference was caused due to the internal formula error

read this article about processor speed on Microsoft

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@ Microsoft mentioned that they have corrected problem in windows 7 and windows 8 but need to check and update my post –  BlueBerry - vignesh4303 Aug 16 '12 at 5:22
    
did you know the act of underclocking/overclocking? –  Deb Aug 16 '12 at 5:28
    
@deb i heard about overclocking and done it at my x2 processor but i am unaware of underclocking –  BlueBerry - vignesh4303 Aug 16 '12 at 5:31
    
@vikki underclocking is done typically on servers to increase the reliability of the machine. to be more specific, i mean to increase the lifespan of the computer. –  chacham15 Aug 16 '12 at 6:57
    
@chacham15 thanks for the explanation –  BlueBerry - vignesh4303 Aug 16 '12 at 7:00
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