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Thread: Can someone explain voltage to me?

  1. #16
    Join Date
    May 1999
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    Vail, CO, USA
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    -> Go to the Asus website, download the manual, read the manual.

    -> Go to the Intel website - there you will find all the white papers on pin assignments for all Pentium CPU's. How you pull the voltage off of the socket is the poser - you might just be able to run the board w/o the CPU.

    -> A CPU uses the same amount of power no matter what the voltage is. Power=voltage*current. Voltage goes down, current goes up. A 100 watt bulb at 120 volts uses around 0.83 amps. A 100 watt bulb at 12 volts uses 8.3 amps. That's why a table lamp can use 18-ga wire, but your KC Daylighters need 12-ga wire and a 20A fuse.
    ...hope this helps...

  2. #17
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    ...there is not a manual for the P2BVE...the P2B-99...is the closest match to ut...one problem...the manual link does not work on the asus site for that model
    Abit KT7A-RAID
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    19" Veiwsoniq PF-790
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  3. #18
    Join Date
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    what happens when you copy the link into your address bar and step back a directory (and/or remove the file name), do you get an index, or just another file? what's the name of the file? if it's listed at .htm, try changing it to .html... whatever, just fool around with it
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  4. #19
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    Jun 1999
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    JL_in_Vail

    Voltage = Current x Resistance

    Since the resistance of your cpu stays the same when you raise the voltage the amperage must also increase.

    Since Power = Voltage X Current when you increase the voltage the power must go up.

    This is why when you keep the same heatsink and you increase the voltage to your cpu your temperature will go up.
    Mike
    Mechanical Engineer
    Dell Computer Corporation
    Server Development

  5. #20
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    Jun 1999
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    Olathe, KS
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    JL_in_Vail,

    -> A CPU uses the same amount of power no matter what the voltage is.
    Dimarini is closer to the truth. Actually, the power is not constant with voltage either. It's a dynamic property of the CPU, that is it's also frequency dependent. The reason is that every time a signal changes state in the CPU, the transistor used in the logic cell (and there may be up to 20+ MILLION of them!) conducts current from the processor core supply to ground. It's a relatively small current, but there are lots of them that add up on each clock cycle. The power requirements of modern CPU's rise with clock frequency because of this.

    Here's a general equation for power consumption in high speed CMOS circuits. Not all CPU's are pure HSCMOS, but the general equation is similar for different fabrication processes.

    Pd = C * f * V^2

    where:

    Pd = Power Dissipation in CPU
    C = Sum of Junction Capacitances in CPU
    f = Operating Frequency
    V = Core Voltage

    Note: C is a constant for a given CPU/Fabrication Process. You can estimate the power increase in your CPU due to increased clock frequency or core voltage without knowing it's exact value, since it doesn't change.

    There is also a constant current draw from the CPU with no clock applied, but it is very low in comparison to the operating (dynamic) current draw when the CPU is clocked at full speed.

    So in general, power increases linearly with an increase in frequency, and is a square of the increase in voltage. If you bump your frequency 10%, then the power will go up 10%. If you increase your core voltage by 10%, your power will increase 21%!

    That is why there is a HUGE drive by CPU designers to lower the core voltages and shrink the geometry of new CPU's. Smaller geometry lets you clock faster and run at lower voltages at the same time. This makes power manageable with reasonable heatsink/fan solutions. It also lets them get more dies/wafer in manufacturing and that translates to $$$ -- lower cost/die for the manufacturer and cheaper CPU's for us!




    [This message has been edited by MGP (edited 08-05-99).]

  6. #21
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    May 1999
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    Hey MGP,
    ...you have now moved beyond my level of knowlege. However, just to save face, remember I did say early on that when increases the frequency of your CPU , you increase power draw. However I willingly accede to your greater knowlege of the inner workings of our mysterious CPUs!
    ...hope this helps...

  7. #22
    Join Date
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    Chicago, IL
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    Whoooaaa! Ummm, thanks guys for the enlightening posts. I DID read everyone of them and, well, the knowledge I've gained is inverseley proportional to the number of posts squared times the difference of members v.s junior members in this thread. Let me be more clear:

    K = 1/(p^2)(m - j)

    K = Knowledge
    1 = 1
    p = posts
    m = unique # of members posting on this thread.
    j = unique # of junior members posting on this thread.

    Oh yes, and K is a constant with the value of 0.

    Actually, I did learn a little. I know you guys were having your own EE discussion and not replying to my question (no worrys!), but what I was really getting at is the relationships between all the of the overclocking components and the effects modifications have on each.

    If I understand it correctly, there are essentially 3 variables in overclocking:

    1) FSB
    2) Multiplier
    3) Voltage

    I am not sure but there may be 2 more:

    4) ratio of speed RAM is running compared to FSB?
    5) ratio of speed AGP port is running compared to FSB?

    Also, I'm sure someone is thinking that temperature is another variable. I agree but since I do not have exact control over the temperature setting of the CPU lets assume that I am using a high-end heat sink/fan combo and that I can't do any better as far as cooling goes.

    Then there are three hardware components that are directly affected by altering these variables:

    1) CPU
    2) RAM
    3) AGP Video Card

    Again, I'm guessing the the PCI/ISA slots are somehow affected by the changes made in our variables. I want to understand how they are affected but would like to save that until last.

    So, I guess you could approach overclocking from 2 angles - CPU or Video. Lets go with CPU because I think OC'ing the CPU will essentially OC the AGP and thus the Video but not the other way around. Is this true?

    This is getting really long so I think I'll just get the ball rolling and add questions as I get responses.

    If I OC the FSB and leave all other variables alone how are all hardware components affected?

    Does everyone see what I'm getting at? I'm thinking that there is a very complex set of relationships between all of these components and variables and I'd like to learn the nature of all of these. That's a tall order and maybe knowing the whole story isn't necessary to OC, but I'm the kind of person who likes to REALLY understand.

    Thanks for reading all the way through! Again, any help is GREATLY appreciated.


    [This message has been edited by Valdin (edited 08-06-99).]

  8. #23
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    If you overclock your FSB you will:

    Overclock your CPU (given)

    Overclock your RAM (some BIOSes will allow you to run ram at AGP speed, but you probably won't want to, just go with good PC100 or PC133 ram from a reputable manuf. micron, siemens, crucial, or corsair)

    Overclock your AGP Bus (Some BIOSes will have different dividers 1/4,1/3 so that your AGP Bus and PCI Bus will run at very close to its correct speed even though your FSB is overclocked)

    Overclock your PCI Bus and all cards plugged into PCI slots. (Some BIOSes .... see above)

    Overclock your ISA Bus and all cards plugged into it.

    Overclock all of the various bridges to usb ports, IDE, etc.

    In a nutshell, depending on your motherboard and bios setup, when you overclock your FSB you overclock EVERYTHING IN YOUR COMPUTER! Unless you have a nice motherboard like a BX6 Rev 2 that lets you run your FSB at 133 MHz with a 1/4 divider so your PCI runs at 33 Mhz.

    [This message has been edited by Dimarini (edited 08-06-99).]
    Mike
    Mechanical Engineer
    Dell Computer Corporation
    Server Development

  9. #24
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    Location
    Chicago, IL
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    Okay, that makes sense. Now, I read posts that say to step up the FSB until you have problems. These posts generally refer to the CPU's temp or limitations in it's ability as the cause of the problems. In reality you have no idea what the cause of the problems are, right? For all we know it could be the PC100 RAM can't handle the boosted FSB. Or the AGP video card now is running at the boosted FSB speed and can't handle it.

    Are there other clocks, buses, whatever on the video card that are independent of the FSB? When people talk about OC'ing the video card they use a software utility to adjust two different settings (I can't remember what they are called.) Are these settings independent from the FSB? If everything feeds off the FSB how can you boost the video settings higher than the FSB?

    Thanks again!

  10. #25
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    The 2 video settings that you refer to are the video memory speed and the video chip speed. They should be independent of the FSB. The FSB is how the various busses in the computer (PCI,AGP,etc) communicate with the processor and memory, the two video speeds are the speeds of the memory on the video card and the chip on the video card.
    Mike
    Mechanical Engineer
    Dell Computer Corporation
    Server Development

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