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Overclocking Help

Discussion in 'Overclocking & Cooling' started by Deckerd, Aug 8, 2007.

  1. Deckerd New Member

    Jun 27, 2006
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    Hi all.

    I am a TPU daily news addict and have recently started to read the forums.

    I need a helping hand on over clocking my PC. I have read some of the guides on here but am still a little unsure of how to OC on my PC, with the specific combination of parts I have.

    I have linked a CPUz screenshot of my CPU.

    I have a Corsair 2 Gig matched pair: TWINX2048-3200C2, running at 2-3-3-6, at T1.
    An Artic Freezer 64 CPU cooler
    A 7800GTX for graphics.
    An Akasa Pax Power 460watt PSU to power my PC.
    The Mainboard is an Asus A8N-E and does have some kind of Auto OC options, like A.I NOS etc but I don't really trust it!

    I don't really know about voltages etc even the relationship between the multiplier, HTT and FSB and how to keep all the components happy with the settings!?

    I bought the CPU off a mate about a year ago and he said he got it running solid as a rock at2.4 GHZ on a stock cooler, mentioned setting the FSB to 240 and lowering the multiplier to x10.

    I don't really want to mess up my PC by doing the OC incorrectly, hence needing a helping hand. I have no clue as to the best settings over even the likely average best speed I might be able to achieve.

    Is it just the CPU I need to OC or do I also need to OC the RAM and GPU to get any benefits? From using the Cool bits software I know I can get my GPU from 415 to 485 and the ram from 1.20 to 1.31 and it seems stable in bench marks etc but I never run with it like that constantly.

    Also just a quick note to explain why I want to OC my PC and to say thanks in advance for any help. I noticed recently that the minimum spec for Bioshock was a 2.4GHZ Intel CPU, MINIMUM! Sounds a little harsh to me but maybe my PC is just getting old? I did think about a cheap upgrade but from best I can tell the current AMD Socket 939 line up of CPU, like the Duel Cores are either not very good for the money or simply cost too much (feel free to correct my perception please). Also it seems a shame not to OC when I have an Arctic Freezer and some performance RAM to try and squeeze some extra performance out of.

    My current games like Company of Heroes and BF2142 all run fine ish but after getting a 20 inch TFT, having to run games in the native 1680*1050 res is starting to show the strain! With all the new games seeming to have high minimum and recommended spec's I'm starting to feel a little left behind.



    Added some pics of my bios options (the setting I am currently using) hope it helps:

    Last edited: Aug 8, 2007
    10 Year Member at TPU
  2. von kain New Member

    Sep 13, 2006
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    welcome to tpu

    i have some head's up go to your bios and find if you can lock the memory,or lower the mem
    to 1/66 so to you memory to be 366mhz (if you can do this you actually minimize the memory problems with overclock) i like the clockgen prog so to check the mhz thru windows plus it can adjust the pci e bus

    my 3200+ 2000mhz manchester reach easy the 2500mhz but for summer stabily i have lower it to 2400 my guess is that 2600mhz for you must be easy
    10 Year Member at TPU
  3. Deckerd New Member

    Jun 27, 2006
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    Thanks for the reply.

    Is that the "Memclock index value" (currently at 400) down to 366, as in the bios pics I just added?
    10 Year Member at TPU
  4. zCexVe


    Apr 25, 2007
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    A64 Mathematics

    One of the most useful tools in my overclocking arsenal is the nGEAR NG-942 electronic calculator. As with most other complicated things in life, overclocking requires some mathematical calculations. The next few sections will take you through all of the important overclocking related calculations used in the future sections.
    Calculating CPU Clock Speed

    Much like how the CPUs of previous platforms ran at a multiple of the FSB frequency, the Athlon 64 overall CPU clock is determined by using a multiple of the reference clock (default of 200MHz). For example, the 1.8GHz Sempron 3100+ uses a clock multiplier of 9 to obtain its default 1800MHz clock speed.

    CPU Clock = Reference Clock * CPU Multiplier

    So if we were to increase the reference clock of this same Sempron to 220MHz for example, we'd have the following:

    CPU Clock = Reference Clock * CPU Multiplier

    CPU Clock = 220MHz * 9

    CPU Clock = 1980MHz

    So really, there are only two variables that will increase your CPU clock speed. Your CPU multiplier, and your reference clock frequency.
    Calculating HTT Bus Speed

    Much like the CPU clock frequency, the overall HTT frequency is also calculated using a multiple of the reference clock frequency. Since the HTT is double pumped, we multiply the entire result by 2.

    Overall HTT Bus Clock = Reference Clock * LDT Multiplier * 2

    For example, the socket 939 A64 chips have a default LDT multiplier of 5, and the default reference clock for all A64's is 200MHz, so we can determine the default HTT as follows:

    Overall HTT Bus Clock = Reference Clock * LDT Multiplier * 2

    Overall HTT Bus Clock = 200MHz * 5 * 2

    Overall HTT Bus Clock = 2000MHz.

    As an additional example, let's assume that we increased the reference clock to 230MHz, and decreased the LDT multiplier to 4.

    Overall HTT Bus Clock = Reference Clock * LDT Multiplier * 2

    Overall HTT Bus Clock = 230MHz * 4 * 2

    Overall HTT Bus Clock = 1840MHz.

    It is important to calculate your HTT bus speed when overclocking. Failure to do so will inevitably put a cap on your system's potential.
    Calculating Memory Clock Speed (1:1)

    When a memory divider is not being utilized, the memory frequency simply operates at the same frequency as the reference clock.

    Calculating your effective memory clock speed in this situation is very simple:

    Memory Clock = Reference Clock

    Note: This formula only holds true when using 'whole' CPU multipliers and no memory dividers. See the below sections for more information.
    Calculating Memory Clock Speed (Using Dividers)

    When using memory dividers, calculating the overall memory clock is not as simple as you may think. People are sometimes surprised to see that their memory is not operating at an expected frequency. It is a common misconception that the memory clock speed is simply a fraction of the reference clock speed. For example, a 5/6 memory divider implies that the memory should operate at 5/6 th the reference clock speed. Although this simple formula does work in some situations, there are also many situations in which it will not.

    The underlying reason is simple: The memory must operate at a clean fraction (integer divisor) of the overall CPU clock speed.

    For example: Assume you have increased the reference frequency to 300MHz, and that you are using an 8x CPU multiplier for a CPU clock speed of 2400MHz. When using a 5/6-memory divider, it seems logical that the memory clock might be calculated as follows:

    Memory Clock = Reference Clock * Divider

    Memory Clock = 300MHz * 5 / 6

    Memory Clock = 250MHz

    However, you may be surprised to find that your memory is only operating at 240MHz not 250MHz. This is clearly not 5/6 ths of the reference clock speed.

    Since we know that the memory must operate at an integer divisor of the CPU clock speed, we need to determine which divisor the memory controller will select. We can do that by using the following formula:

    Divisor = CPU Clock Speed / (BIOS Divider * Reference Clock)

    Divisor = 2400MHz / (5/6 * 300MHz)

    Divisor = 2400MHz / 250MHz

    Divisor = 9.6 <-- not possible to use. Must be a positive integer, so round up to the next integer, which is 10

    Integer Divisor = 10

    So as you can see, to actually achieve 5/6 th of the reference clock a CPU clock speed divisor of 9.6 would be required. This is not a positive integer and therefore cannot be used. The memory controller simply selected the next highest integer. Using a value of 10 allows the memory to run as close as possible to 250MHz without exceeding it.

    Once we know the divisor we can simply calculate the memory clock speed using the below formula:

    Memory Clock = CPU Clock Speed / Integer Divisor

    Memory Clock = 2400MHz /10

    Memory Clock = 240MHz

    Once you wrap your head around them, dividers are not so daunting. Unfortunately, we are often forced to use them especially with chips that have low CPU multipliers.

    TIP: A64MemFreq 1.1, outlined in the Tools section of this article, can calculate your memory frequency for you when using memory dividers. If you are not mathematically inclined, give it a try.
    Calculating the Memory Clock Speed (When Using 'half' CPU Multipliers)

    'Half multipliers' (such as 8.5, 9.5, 10.5 etc) are not 'true' CPU multipliers. You will find yourself getting some bizarre memory behaviour when using half multipliers. Your memory will run at a slightly slower speed than expected. Many people find this puzzling, however when you look at it mathematically it is actually quite simple to understand.

    Your A64 does this simply because your memory must run at a clean fraction of your CPU frequency (just like when using memory dividers). This can only be achieved when 'whole' (integer) multipliers are used. So when using a half multiplier your memory frequency is still running at a fraction of your CPU speed, however that fraction is the next highest whole multiplier value .

    So if you choose a 9.5 multiplier, your memory runs at CPU Clock Speed / 10 , not CPU Clock Speed / 9.5 as you would expect. To calculate your memory frequency when using half multipliers you can use the following formula: (Only applicable when running memory 1:1, i.e. not on a divider)
    Memory Frequency = CPU Frequency / Next Highest 'Whole' CPU Multiplier

    Take a 3800+ processor for example, running at a 2400MHz default clock and a multiplier of 12x. The memory simply runs at '1/12 th ' the CPU frequency as can be seen below:

    Memory Frequency = CPU Frequency / CPU Multiplier

    Memory Frequency = 2400MHz / 12

    Memory Frequency = 200MHz

    If we were to use an 11.5x multiplier on this 3800+ processor, the CPU frequency would obviously decrease. The memory frequency would still be calculated based on the next highest 'whole' multiplier value, which is 12. Therefore, you have a lower CPU clock divided by the same CPU multiplier value, resulting in a lower overall memory clock.

    Memory Frequency = CPU Frequency / Next Highest 'Whole' CPU Multiplier

    Memory Frequency = 2300MHz / 12

    Memory Frequency = 191MHz

    The above theory is good to know, however my simple advice is to avoid half multipliers all together. They unnecessarily complicate things and are usually not required to obtain the best performance out of your A64.

    TIP: A64MemFreq 1.1 outlined in the tools section can calculate your memory frequency when using half multipliers.

    Unlike some Socket A chips, that are completely 'unlocked', AMD's A64 platforms (with the exception of the FX series chips) do not allow free adjustment of the CPU Multiplier. Although these chips are not completely unlocked most of them are not completely locked either.

    Thanks to AMD's implementation of Cool 'n' Quiet technology, the CPU multiplier must be able to decrease in order to reduce the CPU's operating frequency. So any CPU multiplier below the CPU's default multiplier can be selected. This can be very useful when trying to utilize high reference frequencies to push memory beyond the DDR500 mark. Unfortunately, AMD Sempron processors operating at 1.6GHz and lower are 100% locked and cannot be adjusted.

    Below is a listing of CPU multipliers and the chips that utilize them. Most A64 processors fall in the 1.8GHz to 2.4GHz range, with 9x to 12x multipliers.

    Examples of AMD Processors and their Multipliers.

    CPU Multiplier

    Clock Frequency

    Some Retail Examples



    Sempron 2500+ (locked)



    Sempron 2600+ (locked), A64 2800+



    Sempron 3000+, Sempron 3100+, A64 2800+, A64 3000+, Opteron 144, Opteron 165



    3200+, 3000+,X2 3800+, Opteron 146, Opteron 170



    3500+,3700+,X2 4400+, Opteron 148, Opteron 175



    FX-53, 3700+, 3800+, 4000+, X2 4600+, X2 4800+, Opteron 150, Opteron 180



    FX-55, Opteron 152



    FX-57, Opteron 154
    10 Year Member at TPU
  5. Tatty_One

    Tatty_One Senior Moderator Staff Member

    Jan 18, 2006
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    Have a read of one or all of these, at the end you will be an expert!


    This one is good for explaining terminology and functions:


    This one is fairly brief and to the point:


    Good luck!, post here if you have any questions. The post above is helpful and detailed but IMO far too detailed at this stage......learn the basics and terminology, once you have made a start, go more deteiled.
    10 Year Member at TPU
  6. zCexVe


    Apr 25, 2007
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    That is from one of the guys in the net NOT ME.Unfortunately I dont have the link to original guide as I edited it accordingly to the new world and saved as a document.
    10 Year Member at TPU

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