1. This forum section is a read-only archive which contains old newsgroup posts. If you wish to post a query, please do so in one of our main forum sections (here). This way you will get a faster, better response from the members on Motherboard Point.

When is 100% not 100%?

Discussion in 'Overclocking' started by Michael Brown, Dec 6, 2003.

  1. The FPU unit would be far more active at 200FSB as there would be a lot less
    waiting around for main memory. So the heat output of the CPU would rise.
     
    Michael Brown, Dec 6, 2003
    #1
    1. Advertisements

  2. Michael Brown

    ~misfit~ Guest

    I have recently changed my FSB/multiplier on my CPU. It used to run at
    133FSB X 16 multi, 1.825vcore for 2.13GHz. Athlon XP1800+ Tbred-B. I had no
    choice as one of my memory modules (Dual-channel mode) was PC2100 (2 X
    256MB). I now have two PC3200 modules and have changed the settings to
    200FSB X 10.5 for 2.1 GHz and have been able to drop the vcore to 1.80 volts
    and still have it run stably. I see a slight improvement in both CPU and
    memory scores in PCMark 2002. (It won't do 11X even at 1,850 vcore, the
    highest setting available to me without pin-mods, I think I have reached the
    capabilities of my CPU without radical cooling, I'm on air).

    However, running at 100% (SETI and/or Prime95) my CPU temp had gone up
    nearly 5°C compared with 100% load previously with the CPU running slightly
    faster and with a higher vcore. I find this paradoxical. I have since
    rectified the problem at the expense of extra fan noise.

    What would explain this phenomena? Isn't 100% in fact 100%? Would the
    (presumed) faster CPU through-put account for this?

    Just curiousity, I actually expected lower CPU (diode) temps, particularly
    as I was able to lower vcore.

    Thanks for any input.
     
    ~misfit~, Dec 6, 2003
    #2
    1. Advertisements

  3. Michael Brown

    Mickey Guest

    Could it be that the on chip cache is now running at 400MHTZ instead of
    266MHTZ causing the chip to run a little warmer ? This would also increase
    the through put of the chip even at the same speed if it was a bottleneck
    previously.
     
    Mickey, Dec 6, 2003
    #3
  4. Michael Brown

    Ben Pope Guest


    I've found that running Prime95 along with other programs will result in
    less heat production than with Prime95 on it's own. Presumably the context
    switching reduces the load.

    I've always assumed heat production is directly related to voltage and MHz,
    never really thought about it, but it also seem likely that if you end up
    doing calculations faster, you would expect power consumption to increase.
    I would have expected that too, but on memory intensive tasks it would seem
    that the faster memory bus reduces the latency significantly enough to
    enable more calculations and therefore more power consumption.

    Ben
     
    Ben Pope, Dec 6, 2003
    #4
  5. Michael Brown

    Jules Verne Guest

    Did ya clean the processor's heatsink and fan? and the north bridge or
    is it south controller's fan ?? I noticed huge temp drops with a simply
    monthly cleaning of a few minutes with a cotton swap :)
     
    Jules Verne, Dec 6, 2003
    #5
  6. Michael Brown

    ~misfit~ Guest

    Yep. I don't have a 'sink on the southbridge but I clean the CPU/northbridge
    'sinks regularly.

    Thanks.
     
    ~misfit~, Dec 6, 2003
    #6
  7. Michael Brown

    ~misfit~ Guest

    No. The on-chip cache runs at CPU speed, not 400 or 266. So in fact the
    cache is running slower.

    Thanks,
     
    ~misfit~, Dec 6, 2003
    #7
  8. Michael Brown

    ~misfit~ Guest

    I've found the same.
    That seems to be it. I guess if the CPU is benchmarking better (and it is)
    then it must be drawing more current? It just took me by surprise, I've
    never heard this discussed or mentioned and found it strange.

    Thanks for your input.
     
    ~misfit~, Dec 6, 2003
    #8
  9. Michael Brown

    Strontium Guest

    -
    ~misfit~ stood up at show-n-tell, in
    AksAb.21101$, and said:
    I believe that by dropping your core voltage, the processor must increase
    it's work. Back in my K6-2 overclocking days, it was widely seen that
    increasing the vcore, just a bit, would actually decrease max temps...
     
    Strontium, Dec 7, 2003
    #9
  10. Michael Brown

    ~misfit~ Guest

    OK, that sounds feasible. It's just the increase in heat far outwieghed the
    increase in CPU performance (% for %).

    Thanks
     
    ~misfit~, Dec 7, 2003
    #10
  11. Michael Brown

    ~misfit~ Guest

    Ok, food for thought. I may try upping the vcore a little again. Previously
    to running a 200Mhz FSB, every time I increased vcore I got an increase in
    temp.

    Thanks,
     
    ~misfit~, Dec 7, 2003
    #11
  12. Michael Brown

    Ed Guest

    Seems logical, more voltage means the electrons travel faster or
    something like that? ;p
     
    Ed, Dec 7, 2003
    #12
  13. I can't think of a single scientific theory that could predict the CPU
    would 'need to work less hard' with more vcore.
     
    David Maynard, Dec 7, 2003
    #13
  14. Michael Brown

    Strontium Guest

    -
    David Maynard stood up at show-n-tell, in , and
    said:
    Neither can I.
     
    Strontium, Dec 7, 2003
    #14
  15. Michael Brown

    ~misfit~ Guest

    I was hoping for your input into this thread David. What do you think is the
    cause of my CPU running 5°C+ hotter when it's actually running at a slightly
    lower frequency (2.1GHz instead of 2.13) with less vcore (1.80v instead of
    1.825v)?

    The FSB has been increased from 133MHz to 200MHz (finally replaced my old
    PC2100 RAM with two 256MB sticks of PC3200 in dual-channel mode to go with
    my new nForce2 mobo).

    It's nothing to do with a rise in case temps. My CPU is force-fed air from
    outside the case. I'm leaning towards the hypothesis that it's just getting
    more work done due to the higher through-put/FSB speed. 100% before was 100%
    of what it could do within the limitations imposed by the data available.
    Now more data is available to the CPU it can do more work. 100% now is
    probably 105 or 110% of the work it could do before. Therefore more heat is
    produced.

    Make sense?
     
    ~misfit~, Dec 7, 2003
    #15
  16. Well, it's hard to tell because there are a lot of variables. Like, are you
    100% sure there's no change to the average temp of the air coming in? AndI
    don't mean just room temp; changing case orientation (or something else in
    the room) can make a significant difference (changing airflow patterns,
    less airflow, stagnation from nearby structures, etc.).

    The FSB increase, and hence a faster feed to the processor, would sure seem
    to be a source of more processing taking place. That's a potential 50%
    increase in memory bandwidth; just from the FSB. I'm not sure how much more
    you're getting from the dual channel. The vcore change represents only
    about a 2.8% reduction in power.

    But when you say "new nforce2 mobo" that makes me wonder what all has
    changed from the 'old' reading.

    Here's a thought for you. Assuming nothing else changed, perhaps simply the
    act of unplugging and plugging in new memory caused enough of a disturbance
    to affect the heatsink (like maybe the thermal compound contact).

    What was the original temp?

    But yes, I would suspect it's the increase in memory bandwidth increasing
    CPU utilization.

    Btw, I noticed the cache speed comment. What that misses, though, is that
    the FSB buffers, which have to drive the external bus, consume more power
    than internal devices, so an FSB increase would increase the power
    consumption for those buffers. But I couldn't find any numbers to use for
    that in the AMD data sheets.
     
    David Maynard, Dec 7, 2003
    #16
  17. Michael Brown

    Ben Pope Guest

    ICs are all about capacitance... you need to charge each gate to make it
    switch, the more voltage you have the faster you can charge it, once it's
    charged you clock it and wait for the next set of gates to be charged. If
    you do not charge the gates enough (either because you're clocking too fast
    or charging too slowly) then you will get errors.

    Power consumption (and therefore heat production) is directly related to how
    many gates need charging per unit time, and the charge you put on them.
    More voltage = more charge (I think thats a linear relationship, I could be
    wrong it was a while ago). It would seem a bit strange that an increase in
    voltage would decreases temps.

    Ben
     
    Ben Pope, Dec 7, 2003
    #17
  18. Michael Brown

    Strontium Guest

    -
    Ben Pope stood up at show-n-tell, in
    bqv6qd$25v0fs$-berlin.de, and said:
    Yes, I agree. I was, merely, stating an observation that seemed widespread
    with the K6-2+'s... Of course, this is from memory, nothing more. Perhaps
    I should have been a bit more specific, in my prior comment. It seemed (or
    so it was reported) that once overclocked, a very small (0.1-0.2V) increase
    in core voltage dropped the temperature (which had, consequently, increased
    due to the initial overclocking) by about 1-2degC. Obviously, this can be
    attributed to measurement error/variation, etc... However, from what I
    remember, it was pretty consistent. And, at a certain point, raising the
    core had detrimental effects (for obvious reasons).

    I'm of the opinion that not everything in the universe is
    known/fathomed/figured out ;) Then, again, it's been over ten years since
    I've studied PChem/Quantum Mechanics and Physics. So, perhaps, I should've
    just kept my fingers shut.

    I've jumped the AMD ship, in the past year, so it's really academic to me
    anyway. And, as usual, I'll leave the disclaimer that my memory is not what
    it used to be, yada, yada...
     
    Strontium, Dec 7, 2003
    #18
  19. Michael Brown

    Ben Pope Guest

    I understood that it was from observation and I do believe you, I was just
    thinking aloud really to see if I could come up with a reason... the best
    one so far is that the increased current drain from the processor reduces
    the voltage on the sensor, so when reading it back the temperature seems
    lower. (not a very good theory :)
    This is a public forum, say what you like :)

    Ben
     
    Ben Pope, Dec 7, 2003
    #19
  20. Michael Brown

    Hippy Paul Guest

    I have observed this increase in temperature with a higher fsb compared to
    upping the multiplier (and have mentioned it in other posts) - I just put it
    down to the fact that by increasing the fsb you are making memory related
    things run faster as well as fsb things and subsequently they give off more
    heat. - technical or what
     
    Hippy Paul, Dec 7, 2003
    #20
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.