CPU Speed - why does it change?

[John Smith]

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

Have just discovered I seem to be working with two different CPU speeds...

1.about 1830MHz when the sides of the computer are ON (the Barton's spec is
1883MHz so thats ok), and
2. about 1075-1095MHz when the sides are OFF

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 up at 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)

voltage - 1.648v (1.664)
Multiplier - 11 (11)
FSB - 166.4 MHz (99.5)
Bus Speed - 332.7 MHz (198.9)
Core speed - 1830 MHz (1094)

Again...does that seem reasonable?...Its baffled me

Any help would be appreciated.
Thanks,

 

[YKhan]

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

Have just discovered I seem to be working with two different CPU speeds...

1.about 1830MHz when the sides of the computer are ON (the Barton's spec is
1883MHz so thats ok), and
2. about 1075-1095MHz when the sides are OFF

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?

When you're talking about the "sides of the box", are you talking about
the case doors?

Yousuf Khan

 

[John Smith]

When you're talking about the "sides of the box", are you talking about
the case doors?

Yousuf Khan

 

[YKhan]

Hmm, did you build the system yourself, or was it bought ready-made? Do
you have a case fan mounted on the case cover itself? If so do you have
to unplug it prior to completely opening the case? Another possibility
is some kind of a switch on case frame that detects when the case cover
is in place?

Yousuf Khan

 

[John Smith]

Hmm, did you build the system yourself,

Yes..well virtually totally upgraded a couple of years ago.

Do
you have a case fan mounted on the case cover itself?
No

Another possibility
is some kind of a switch on case frame that detects when the case cover
is in place?

Can't see one of those...but wouldn't know what to look for.

Looking at it this way...if I wanted to - how could I change the FSB/Bus
Speed...what changes them?
Thanks.John

 

[George Macdonald]

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

Have just discovered I seem to be working with two different CPU speeds...

1.about 1830MHz when the sides of the computer are ON (the Barton's spec is
1883MHz so thats ok), and
2. about 1075-1095MHz when the sides are OFF

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 up at 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)

voltage - 1.648v (1.664)
Multiplier - 11 (11)
FSB - 166.4 MHz (99.5)
Bus Speed - 332.7 MHz (198.9)
Core speed - 1830 MHz (1094)

Again...does that seem reasonable?...Its baffled me

Any help would be appreciated.

I'd first want to confirm what MBM is saying. Have you checked with
Windows XP(2000?) System Control Panel to see if it gives the CPU clock
speed - if not then DXDiag should show it. How about Power Options Control
Panel... does it show a Power Now Tab? Do you have the AMD PowerNow driver
loaded?

This has nothing to do with the CPU per se - the FSB is getting lowered and
that's down to the clock chip and its control. As to why that would be
tied to the case covers, as Yousuf says, the only thing I can think of is a
chassis intrusion switch. Check in your BIOS Setup for such a control to
see if it's Enabled or not. Check your mbrd docs for a chassis intrusion
jumper - most people just leave that jumpered but that's where a chassis
intrusion switch would be connected to.