Tom's Hardware > Forum > CPU & Components > CPUs > CPU clock speed - why does it vary?

CPU clock speed - why does it vary?

Forum CPU & Components : CPUs - CPU clock speed - why does it vary?

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ojcactus   05-09-2006 at 07:46:09 PM

Hi,
I'm not too familiar with the workings of cpu...so I'd be glad for any comments/advice ref the following.

Abit motherboard NF7-S and Athlon XP 2500 Barton cpu

I had been under the impression ...clearly wrongly..that the speed of a
cpu under normal use was pretty well constant?
Made a note in Motherboard Monitor (MBM) of the cpu speed with sides of
the box off = 1094 MHz...with sides on this jumps to 1796MHz !
Is that what could be expected, and if so how come?

And further...from start up and with sides off and cpu speed showing 1093MHz and board
temp 29C and cpu temp 42C
I then put back on the sides, and, after 40mins temp rose to 36C and
48C but cpu speed still showing 1093!?
Then turned off the pc..then straight away turned on the pc and find temps
39 and 53 and cpu speed now 1829!!...does that make sense?

...and lastly Just checked the following when sides on and sides off via cpu-z:-
with sides on first (and sides off)
Core speed - 1830 (1094)
voltage - 1.648 (1.664)
Multiplier - 11 (11)
FSB - 166.4 MHz (99.5)
Bus Speed - 332.7 MHz (198.9)
Again...does that seem reasonable?..and why?
Thanks,

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strangestranger   05-09-2006 at 08:18:08 PM
- 0 +

are you sure its not the cpu's fan speed that you are looking at? unless it has a cool and quiet feature it won't be changing and the side panel of you case being off will make no difference. if it is you cpu fan, it sound like you have bad air circulation.

Reply to strangestranger
Pain   05-09-2006 at 08:18:33 PM
- 0 +

Sides off, sides on?

Well, I suggest you get a dead chicken and some crows blood, cause there's strange voodoo happening in your machine.

Reply to Pain
dorion   05-09-2006 at 08:18:52 PM
- 0 +

Well I know that the mobile Athlon XPs had AMD PowerNow the little brother of CoolnQuiet. But that varies the Multiplier. And Thermal Throttling is in P4s if I remember right. Maybe your motherboard is underclocking your CPU when it hits a certain temperature? That could explain why it drops when the sides off, taking off the sides of your case could disturb the flow of air enough... maybe.

Reply to dorion
Anoobis   05-09-2006 at 08:57:18 PM
- 0 +

I keep wanting to think it's some sort of case intrusion setting, but I do not recall the NF7 having a header for this feature. I know some Asus nForce 2 boards had them. Who makes your case? It could be possible it has a case intrusion feature on it which could be causeing this.

Reply to Anoobis
ojcactus   05-10-2006 at 03:48:49 PM
- 0 +

No, I'm pretty sure its the cpu speed...at least both MBM and cpu-z says so.
Its a mystery.....:-

Sides OFF: Bus speed=199MHz, FSB=100MHz, Multiplier=11,
Core speed=1094MHz and volts = 1.664

Sides ON: Bus speed=333MHz, FSB=166MHz, Multiplier=11,
Core speed=1830MHz and volts = 1.648

Reply to ojcactus
strangestranger   05-10-2006 at 03:54:20 PM
- 0 +

OMG that ain't right. see if the other poster was right in that an intrusion detector is there. there should be a wire that leads to you mobo. i've never heard of this yet on my time on these forums. interesting and id like to know what is causing this. is there any buttons on the case where the side panel meets it.

Reply to strangestranger
ojcactus   05-10-2006 at 03:57:08 PM
- 0 +

Mmmm.case intrusion setting - hadn't thought of that possibility.
I'll have a look - no, don't think so - at least can't see anything.

Reply to ojcactus
strangestranger   05-10-2006 at 04:09:44 PM
- 0 +

forgot to ask what case you have.

Reply to strangestranger
fainis   05-10-2006 at 04:17:34 PM
- 0 +

hmmm..interesting..............barton.......never heard about cool&quiet on barton............

Reply to fainis
Anoobis   05-10-2006 at 08:51:35 PM
- 0 +

dorion was talking about AMD PowerNow Tech which was available for use on the Athlon XP Mobiles. It's one of the reasons the chips came unlocked from the factory.

Reply to Anoobis
ojcactus   05-10-2006 at 11:45:11 PM
- 0 +

forgot to ask what case you have.


Standard run of the mill full tower.

Reply to ojcactus
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