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Overclocking and stability

Traditionally for Asustek's motherboards, power supply is made on two-channel scheme and contains four condensers of 3300uF each and three of 1200uF each.

I don't have any complaints on stability of the board. Asus A7V8X have undergone a number of tests and was working in different modes. I draw the following table for better understanding.

* - As soon as new AMD processors working at 166MHz have been issued, this mode becomes supported officially.

I was using Athlon XP 1600+ processor with locked clock multiplier in all of stability tests. Certainly if the multiplier is unlocked, much better results can be achieved.

Overclocking capabilities:

Firstly, this is a variation of the multiplier. This parameter can be varied in a range from 5 up to 22.5 with a step increment of 0.5. Pay attention to the rather high maximal value of the multiplier (22.%). All KT333 based boards, which I have tested before supported maximal multiplier of 14. This was achieved, as a rule, due to mixing of two multipliers (e.g. 5 and 14). I was met by some emergencies when processor was either refusing to start with a small value of clock multiplier or was starting but had been incorrectly determined by a board. Thus we can see a certain progress when KT400 is used.

Here we have an opportunity to set FSB clock from 100MHz up to 227MHz with 1MHz step increment. ICS 94228BS chip was used as a clock generator.

Here we can't see any advantage of KT400 in comparison with its predecessors. As I have told before, new AGP and PCI frequency dividers were not actualized in KT400. As the result, the maximal possible divider for PCI equals 1/5 (2/5 for AGP). This leads to the following: frequencies of 200MHz and higher will be used by extreme overclockers only.

But if 1/6 divisor was actualized, KT400 might have conquered a great popularity. Look, we take a new Athlon XP Thoroughbred (0.13um) and unlock its multiplier with a single stroke of a pencil. Then we set FSB clock to 200MHz and set synchronous mode (FSB:MEM - 1:1) with DDR400 memory (at this PCI clock would have been 200/6=33MHz). We have a superproductive and stable system with relatively few financial expenses. But these are the dreams, which will come true with a new revision of KT400 (according to the performance of today revision, the new one must do it).

By the way, I have noted a very interesting feature: when FSB clock is changed, boot-up screen displays "native" CPU clock ("native" CPU index in case of Athlon XP). Moreover, wcpu utility was also displaying starting frequency.

I wonder if other KT400 boards will have the same ability. But actually, it looks like BIOS feature and this function does not depend on a used chipset.

The most interesting thing happened when I installed Windows XP at FSB clock of 166MHz after experimenting with overclocking. This moment renders very high stability of the motherboard.
Then, maximal possible Vcore range is necessary for successful overclocking. Documentation of Asus A7V8X informs that there is a default possibility to change CPU voltage from 1.5V up to 1.85V with a step increment of 0.025V. For those users who need a wider range, there is an OVER_VOLT jumper. If it is repositioned, Vcore upper limit is raised up to 2.05V.

But in practice, changing this jumper didn't lead to positive result. Maximal operational value of Vcore remained at 1.85V.

Probably this drawback of BIOS will be corrected in the future.

After I have updated last version of BIOS on the 13th of September, "CPU Vcore" values remained the same (1.75V - 1.85V). But during operation, the board was increasing the voltage by 0.2V, which lead to maximal possible Vcore value of 2.05V.

I have a couple of remarks more. After I have installed Duron processor, Vcore range became 1.55V - 1.75V. Changing position of OVER_VOLT jumper hadn't changed anything. Maximal Vcore value remained at 1.75V. As the result, I received maximal possible FSB frequency with Athlon XP with blocked multiplier. Anyway Duron processor is out of date. Applying a processor, which works at less than 1GHz and at 100MHz FSB, to such board is a sin :)

So, the set of overclocking opportunities is rather powerful. And results prove to be very good. As you can see on the screenshot of Wcpu, overclocking is very successful. The actual frequency of 1890MHz matches the index of approximately 2300+ - +2400.

There is one more note, overclocking results depend on output of power supply. I test almost every motherboard with quite weak 200W power supply of Genius Venus case and average 250W (but qualitative) PowerMan of Inwin case. On A7V8X board, maximal FSB clock reached 170MHz with the former case and 180MHz with the latter one. Also the processor was heating less with Powerman (it was cooler on 5-8 C = 9-14 F ). Summarizing entire information I may conclude that KT400 based boards need very qualitative power supply.

By the way, look how Shuttle engineers solved the problem of power supply with their last AK37GTR board (This motherboard preview is under development and is coming soon).

Let's get back to our board. Asus A7V8X support the function of changing memory voltage. Available values are "Auto", 2.55V, 2.65V, 2.75V and 2.85V. Unfortunately I couldn't determine what is hidden under name "Auto". Motherboard Monitor program doesn't work with this board and native PCProbe utility doesn't do this either.

And finally an overclocker has an option to increase AGP voltage. Available values are 1.5V, 1.6V, 1.7V and 1.8V.

Unfortunately there is no possibility to increase voltage on I/O circuits. However this could demand more powerful chipset cooling (i.e., an extra fan).

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