CPU clock speed - why does it vary?

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?
8 answers Last reply
More about clock speed vary
  1. 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.
  2. 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.
  3. 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.
  4. 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
  5. 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.
  6. hmmm..interesting..............barton.......never heard about cool&quiet on barton............
  7. 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.
  8. forgot to ask what case you have.

    Standard run of the mill full tower.
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