New AMD Duron Overclocking Guide

by FastSite
03/12/2001 | 12:00 AM

Quite a lot of time has passed since we posted our latest review dedicated to AMD Duron overclocking, but still these CPUs remain indisputable favorites among overclockers. And it's not for nothing, we should say. The main reason is that Duron CPU - and especially the younger models - still remain the most overclockable processors. You can easily find a Duron working at about 1GHz among both: already discontinued Duron 600 and Duron 650 CPUs and brand new processors. As practice shows, a 50% frequency gain is not an extraordinary figure for Duron CPUs. Brilliant results like that have never been achieved by any other processors, that are currently available on the market. Thus, the maximum for AMD Athlon is a 200MHz frequency increase above the nominal value. Pentium III follows the trend as well. As for the former overclocking leaders, Intel Celeron processors, they lost their dominance when the new models of the line appeared. So, now it's become a pretty rare thing that a Celeron works at 100MHz FSB. And the freshly made Celeron 800, which was originally intended for 100MHz FSB, can't boast better overclockability than the elder Pentium III model. All this lets Duron stay the best alternative for overclockers. For the time being, Duron is one of the cheapest CPUs and at the same time it demonstrates pretty good performance both in office applications and 3D games, so you may find it worth trying to squeeze the juices out of this processor to make it work at over-nominal frequencies and this way to save a plum sum.<%BANNER[article]%>

Actually, we have just repeated what we always said in our previous articles. If you are interested why we decided to continue discussing this topic, you are welcome to read further.

Overclocking: Multiplier vs FSB

After AMD Athlon CPUs with 266MHz FSB were announced in October 2000, a number of chipsets officially supporting this bus was also launched. These were AMD-760, ALi MAGiK 1 and VIA KT133A. As soon as we got hold of mainboards based on these chipsets, a curios fact came out: formerly Socket A processors didn't allow overclocking not because of the processors themselves, but because of the "imperfection" of the older chipsets, AMD-750 and VIA KT133, that officially supported only 200MHz CPU bus (or 100MHz FSB). Subsequently, the same AMD Athlon and Duron processors designed to support 200MHz bus, which could not go further than 110-115MHz FSB on VIA KT133 based mainboards, made a welcome change in overclocking when we tested them on new boards. Overclocking Socket A processors on AMD-760, ALi MAGiK 1 and VIA KT133A based mainboards by means of increasing the FSB frequency proved much more fruitful. I this case FSB frequencies could be increased up to 133MHz and even higher. So, it was for the chipsets, but not the CPUs that FSB frequencies were hard to raise. As a result, you can now simply increase the FSB frequency to overclock those processors that used to be overclocked only with the processor clock multiplier (this is what we discussed in detail in the previous article). That's why we made up our mind to offer you another article on Socket A CPUs overclocking (namely AMD Duron, although all the ideas also work for Athlon processors), where we compare the overclocking with the help of FSB and clock multiplier to see, what troubles an overclocker may face while dealing with FSB frequency.

But first let's clear out, whether it makes sense to try FSB overclocking with Socket A processors. For this purpose we took AMD Duron 600MHz, which is famous for its really good overclockability. First, we checked what frequency gain we could get by increasing the clock multiplier (FSB was locked at 100MHz), and then we increased FSB frequency (this time the multiplier was locked at 6.0x). The experiment was run on a VIA KT133A based platform supporting PC133 SDRAM and CPUs with 266MHz bus. We decided not to use DDR mainboards, since DDR SDRAM is too expensive for broad masses of users yet, so its price contradicts the very idea of overclocking, i.e. getting higher performance for less money.

The results of this investigation are available on the chart below:

To obtain the frequencies of 700, 800 and 900MHz, we took the FSB frequencies of 117, 133 and 150MHz correspondingly. Unfortunately, the system's work was unstable at 166MHz FSB required to reach 1GHz for the CPU. For this reason, the highest result we took in this case was 960MHz CPU frequency (instead of 1000MHz) at 160MHz FSB.

Nevertheless, it comes clearly from the diagram that FSB overclocking is more effective. The trick is that the performance in office applications, which is measured by SYSmark 2000, is determined not only by the clock speed of the CPU, but also by the fastness of the memory. Since all the currently existing chipsets for Socket A CPUs have memory, heavily influenced by FSB frequency, higher front bus frequency leads to an increase in the memory working speed. If we use only clock multiplier, it doesn't affect the memory subsystem anyhow. That is the reason why FSB overclocking is better than merely using a multiplier.

Now let us see, how greatly the performance grows by overclocking, if we test in 3D games:

In Quake3 the gap between the CPUs overclocked in two different ways is even greater. It happens because, first, Quake loads the system more than typical office applications do. By the by, that's why the performance gain, achieved by overclocking with the multiplier, shrinks as the CPU frequency grows. The constant memory frequency equal to 133MHz doesn't suffice to provide enough data to the CPU that works at higher frequencies.

Furthermore, as soon as the FSB frequency exceeds 133MHz, increasing the AGP bus frequency over the nominal values produces a favorable effect as well. AGP bus working at higher frequencies allows achieving higher CPU frequencies when we overclock it by increasing the FSB speed.

The graph line showing the performance by FSB overclocking plunges slightly at 800MHz, because before this point the memory frequency totaled FSB+PCI, and starting with 133MHz FSB (needed to achieve 800MHz CPU frequency) the memory was clocked at the same level as FSB. The phenomenon can also be partially explained by the impossibility to make the memory frequencies on most KT133A-built mainboards equal to FSB+PCI when the FSB frequency exceeds 124MHz.

This way, since overclocking the CPU by means of clock multiplier affects only the processor core, this method is less effective than overclocking by means of increasing the FSB frequency. The matter is that when FSB frequency is increased, it doesn't only overclock the CPU core but also brings about a notable throughput growth of the basic subsystems: memory and AGP subsystems in the first place. That makes it reasonable now to focus on raising the FSB frequency, but not the multiplier while overclocking Socket A processors.

The question is how to overclock AMD Athlon and Duron CPUs to obtain the highest performance on the new mainboards supporting 266MHz FSB? Well, there is nothing complicated about that if you look through the above given ideas one more time. An overclocker should concentrate on squeezing as much as possible from the FSB. Moreover, it may be necessary even to sacrifice the clock multiplier and to lower resorting to methods like those described in our AMD Duron Overclocking Experience. But still, please, try not to go overboard. For instance, it is evident that if the system works stably at 969MHz CPU frequency obtained as 6.5x149MHz, but some troubles occur when you set 6.5x150MHz or 6x151MHz, then it is unreasonable to set the CPU as 6x150MHz=900MHz, because the additional 69MHz of core frequency are sure to provide greater effect than the extra 1MHz for FSB.

Now we would like to give you some general recommendations on how you'd better assemble and adjust a Socket A system to overclock the CPU more successfully.

133MHz FSB Frequency

To start with, we will touch upon the easiest and so the least troublesome way to overclock an AMD Duron CPU up to 133MHz FSB. For new mainboards based on VIA KT133A chipset, AMD-760 and ALi MAGiK 1, it is a nominal frequency. So, the processor will be the only component of the system to work at over-nominal frequency when the FSB works at 133MHz. A pleasant thing is that, according to our practical experience, all CPUs intended for 200MHz bus (and 100MHz FSB) feel well at even much higher FSB frequencies than 133MHz. So, it should sound encouraging for the one, who is about to overclock Duron (or Athlon supporting 200MHz bus) by increasing the FSB frequency.

Then comes another question: is it worth trying this kind of overclocking at all? You know, it is quite possible to overclock the core without tackling the FSB, especially since the frequencies of the memory and AGP aren't affected at all in this case. Mainboards built on VIA KT133A, which are most commonly used for Duron overclocking, ensure the following FSB to memory frequencies ratios: 100:100, 100:133 and 133:133. So, it may seem that if we treated the CPU when the FSB frequency is set to 100MHz and the memory frequency to 133MHz, we would get the same performance. We could back up this conclusion by the fact that the CPU bus bandwidth in a system like that would be definitely higher than that of the memory bus and hence wouldn't become a bottleneck even if it worked at 200MHz. However, this nice idea proves to be false.

The thing is that if FSB frequency is increased up to 133MHz, we can have the memory running at 133MHz as well synchronously with the CPU bus. This mode is more fruitful than the asynchronous one, for the memory controller doesn't have to add more wait states to match the signals that come from the CPU and the memory. To illustrate this process, we have measured the real memory bus bandwidth in a Duron based system when the CPU was clocked up to 1GHz with 100MHz and 133MHz FSB.

We believe that no comments are neededá the chart shows everything pretty well: 133MHz FSB is more preferable than 100MHz FSB. Of course, you may need to make use of the clock multiplier to complete the entire overclocking process at 133MHz. By the way, when you overclock AMD Athlon and even elder AMD Duron processors, for the sake of setting the FSB to 133MHz you may have to lower the clock multiplier because the CPU can't work at a frequency, that exceeds the nominal by 33%. For this reason you should unlock the multiplier. To do it, you should close four L1 Bridges on the top of your CPU, using one of the methods described in this article.

We wish we could predict the overclocking limits of each particular CPU. AMD Duron processors that are manufactured within different timeframes differ tangibly in their overclockability, although they have similar nominal frequency. We have tested a big number of Duron CPUs of different series, so we can provide some statistics for you to figure out, what to expect from a CPU, according to its marking. A table with this precious data is available here:

150MHz FSB Frequency

As you can see, there is nothing extraordinary about overclocking the FSB to 133MHz. Things appear much more complicated when we go further. As the FSB frequency gets higher than the nominal 133MHz supported by the new Socket A chipsets, the memory, AGP and PCI frequencies go to over-nominal heights as well. The memory frequency corresponds to that of FSB, AGP bus works at FSB/2 and PCI at FSB/4. It means that, for example, when you set FSB at 150MHz, the memory works at the same frequency of 150MHz instead of the original 133MHz, AGP shows 75MHz versus 66MHz and PCI reaches 37.5MHz instead of 33MHz. Therefore, if you clock the FSB higher than 133MHz, it's essential to use quality bundles that can function stably and reliably at over-nominal frequencies.

However, even if some system components don't work stably enough as FSB frequency grows, you may improve the situation with the help of BIOS Setup of your the mainboard. For instance, if the memory suffers some freaks, you may increase CAS Latency up to 3 and risk only a 2-3% performance drop, getting a more stable system instead. Sometimes increasing Vmem can also come in handy, but the upsetting point is that not all mainboards provide this opportunity. If it is the graphics card that reacts badly to overclocking, you may try to disable AGP 4x mode that hardly tells on the performance. And surely you should increase Vagp.

Now let's discuss a really grave problem that may stand in the way when you try to overclock your AMD Duron CPU by means of the FSB frequency increase: the boards and the chipsets. As it used to be earlier, even after the launching of chipsets supporting 266MHz CPU bus, the major predicament for overclockers is the core logic. The only difference compared to the previous times is the upper limitation that has moved towards higher frequencies. Surprising as it might seem, but the CPUs designed to support 200MHz bus have proven to be able to work successfully at the FSB frequencies far beyond 150MHz.

If we take no extra measures, the top FSB frequency that can be squeezed from the best mainboards based on VIA KT133A (as well as other new chipsets, actually) will equal to 140-145MHz. It's noteworthy that, perhaps, such a system will work well at higher frequencies too, but as a rule the stability of this system leaves much to be desired. You can see it by running several resource-hungry applications at a time. To achieve higher frequencies, you will have to make a few special things.

The first thing to contribute to successful overclocking is proper chipset cooling. As we tested the boards on VIA KT133A, we noticed that their North Bridges get heavily overheated. Sometimes the temperature rose up to 60 degrees. Our experiments showed that in case neither the memory, nor AGP and PCI cards have problems working at over-nominal frequencies, the proper cooling of the chipset North Bridge can grant a 5-10% FSB frequency increase with no stability losses. This way, if you have extreme overclocking plans, make sure that the heatsink on your chipset is equipped with a good fan and add a layer of thermal paste between the heatsink and the chipset.

You can win 5-10MHz more while overclocking the FSB, if you increase the chipset Vio. Of course, as the chipset voltage goes up, the chipset begins to dissipate more heat. So, you will have to give way to the warm air flow coming from the chipset North Bridge, which could be achieved by installing an extra cooler into the PC case, for instance.

To sum it up, the key to 150MHz and higher FSB frequencies lies not only in high-quality memory and add-in cards, but also in good cooling of the chipset North Bridge and Vio increase. Surely, the mainboard layout and mounting matter a lot too, but this issue will be brought up in the next part of the article.

How to Choose the Best Mainboard for Overclocking Needs?

It is high time we passed over to concrete recommendations. We will try to figure out what specifications a mainboard used for Socket A processors overclocking by means of increasing the FSB frequency should have.

First of all, if you want to be able to set FSB frequency higher than 110-115MHz, which is in fact the top limit for mainboards built on older VIA KT133 and AMD-750 chipsets, the board should be based on a core logic officially supporting CPUs with 266MHz bus. Among them are VIA KT133A supporting PC133 SDRAM, and two DDR chipsets: AMD-760 and ALi MAGiK 1. Although we will give only general recommendations concerning the choice of your mainboard, we'll keep in mind basically VIA KT133A based products. The thing is that this core logic supporting PC133 SDRAM is the best alternative so far for systems boasting the most optimal price-to-performance ratio. Ad for DDR memory, it is still too costly and is not that widely spread yet, as a result.

Now, what other features are vitally important for the overclocker's choice of mainboards?

Here is a list of necessary features:

• Changing the FSB frequency with small increment. It goes without saying, that the smaller is the increment, the "finer" adjustment of the overclocked CPU the board supports. That's why you should pay special attention to those boards, which offer an increment of 1MHz and thus allow you to sweat the CPU to the greatest extent possible. There is the whole bunch of boards like that on the market, since many manufacturers have learned to provide their products with clock generators, which let you set any frequency you like within a certain range. The most well-known boards of the sort are those by ASUS, ABIT, Iwill and MSI.
• High-quality mainboard design. Since the bus of Socket A processors uses DDR technology, i.e. it transfers the data along both signal edges, the data stream between the CPU and the chipset goes with twice the FSB frequency. That is why all mainboards for AMD Duron and Athlon processors should have clever design and layout. Of course, it's pretty hard to estimate at a glance, whether the board layout and the mounting are good or not, however, as we all know, brand name products are usually of higher quality than the other ones. Moreover, in order to minimize the traces between the chipset, CPU and memory and thus aiming at higher stability, most manufacturers have recently started rotating the North Bridge microchip by 45 degrees relative to Socket A. Subsequently, it is the most preferable location of this microchip then.
• Changing the CPU clock multiplier. Although we deal with overclocking processors with the help of FSB frequency only, the possibility to change the clock multiplier of the CPU remains an essential condition. To say more, you may need either to increase the multiplier (e.g. if the CPU can theoretically work at a higher frequency, but the FSB is impossible to raise because of the mainboard, the memory, the graphics card or some external devices) or to lower it (if you face a roundabout situation: the CPU has reached its top frequency, but all the other components of the system can endure higher FSB frequencies). At the same time, don't leave out the fact that before changing the CPU clock multiplier, you should unlock it. For this purpose you need to close L1 Golden Bridges on top of the CPU (for details click here).
• Changing CPU Vcore. It's one of the major functions that allow you to increase the stability of the overclocked CPUs. If you care for the best results with a minimal risk to wreck the processor, the best way is to increase the Vcore by 0.2-0.25V. However, unfortunately those mainboards, which allow changing processor Vcore within a narrower interval or which do not have this opportunity at all, will prevent you from overclocking your Duron to the full extent.
• Changing chipset Vio. This feature is not less important for CPU overclocking by FSB frequency increase than all the previously listed ones. According to our tests, the safety limit is 3.9V. It provides a 5-10MHz FSB frequency gain and ensures stable work of the chipset in this case.
• Proper chipset cooling. As the FSB is clocked up, the North Bridge heats quite a lot. If this microchip is not properly cooled, it gets overheated and can cause the system to crash. So, an active cooler on the chipset is important for the mainboards, that are meant to be used for CPU overclocking by increasing the FSB frequency. Furthermore, there should also be a layer of thermal paste between the heatsink and the chipset, so that to improve heat dissipation. At least you should never resort to a sticky pad with no heat-conductive qualities, though it appeals to many mainboard manufacturers. The best way to fasten your cooler is by means of a few spring clips, which is much more efficient for good cooling rather than simply sticking a cooler to the chipset surface.

The boards are also welcome to:

• Allow changing Vagp. Sometimes it may help to increase the system stability when it works at non-standard AGP frequencies. Indeed, most graphics cards have no problems working at over-nominal AGP frequencies. Moreover, you may simply enable 2x mode to the AGP bus instead of raising the Vagp.
• Allow changing Vmem. This may contribute to better stability of the memory subsystem as it works at over-nominal frequencies. It makes sense to resort to this option only if all the other measures, including setting CAS Latency equal to 3, have no desired effect.

Testbed and Methods

In order to supply some practical data about AMD Duron overclocking, we compared the performance of several systems, including those with AMD Duron, which was clocked up to 1000MHz in different ways. 1000MHz frequency seems to remain the maximum a Duron processor can now achieve. Evidently, this limitation is caused by the manufacturing technology, since Duron CPUs are manufactured in Austin with aluminum interconnect technology. In their turn, all Athlon processors with the working frequencies over 1000MHz are manufactured in Dresden, where all the CPUs are made with copper interconnect technology. This way, although sometimes one can luckily find a Duron capable of overclocking up to 1050MHz, we wouldn't hope to find one like that, if we were you. The most probable top for extreme Duron overclockers still remains 1GHz.

We overclocked Duron CPUs up to 1000MHz in three ways:

• 10x100MHz is a standard way, also applicable for older mainboards that lack 266MHz CPU bus support. Here, all the devices and the memory work at nominal frequencies.
• 7.5x133MHz is a common way as well, but it is used only for new mainboards built on VIA KT133A, AMD-760 and ALi MAGiK 1 core logic. The memory, various PCI devices and AGP graphics cards work in the nominal mode.
• 6.5x154MHz is extreme overclocking, when FSB frequency should be set at its maximum. In this case we also clock up the memory (it works at 154MHz now), the PCI bus (38.5MHz) and the AGP bus (77MHz).

To overclock a Duron up to 1GHz we had to increase the Vcore up to 1.85V (instead of the nominal 1.6V). In order to ensure the stability of the entire system at 154MHz FSB, we increased the Vio up to 3.9V (that is 0.6V higher than the nominal voltage). As the FSB was overclocked to 154MHz, we faced some troubles with the graphics card and were forced to enable AGP 2x mode.

As for the mainboard, our preferences stayed with ABIT KT7A. It seemed to suit us, since its predecessor, ABIT KT7 (a mainboard based on the ancient VIA KT133, but with the same PCB design), proved to be one of the most stable boards for Socket A processors. Then, ABIT KT7A built on the new VIA KT133A core logic meets all of the above listed requirements.

The last thing to add is that we took AMD Duron processor with 800MHz manufactured on 51st week. Please, keep in mind that the obtained results do not depend on the processor nominal frequency and can be obtained on any CPU with the potential overclockability up to 1GHz. Moreover, as it follows from the AMD Duron overclockability table, the top frequency, which is reached by different CPUs of the family, doesn't seem to depend on either the nominal frequency of the processor or on the date, when it was manufactured. Thus, choosing a processor becomes a sheer lottery.

We tested on three platforms: one based on AMD Duron, another on AMD Athlon and one more - on Intel Pentium III, all of them working at 1GHz. The Athlon CPU performance was measured with FSB frequencies equal to 100 and 133MHz, while Pentium III worked only with 133MHz FSB. The testbeds were configured as follows:

We tested in Microsoft Windows 98 SE.

Performance

Here comes one of the most interesting parts of our investigation, where you'll see how fast the overclocked AMD Duron CPUs are in real applications. Traditionally, we start with the performance demonstrated in office applications and then it will be the turn of 3D games.

The performance in basic business applications, which is shown by this benchmark, depends on three main factors - the memory latency, the capacity and fastness of L2 cache and the HDD. Other determinants are less important for the results of Business Winstone 2001. That makes the final scene look not surprising at all. AMD Athlon is faster than the Duron, which works even at 154MHz FSB, for it has a fourfold greater L2 cache. Pentium III brings about no disappointing news as well: its L2 cache is also bigger than that of Duron CPUs, and its smaller L1 cache is compensated by a faster bus between the core and the cache. Generally speaking, in business applications the 7% difference in the performance of Duron processors, which were overclocked in different ways (with the FSB frequency and the clock multiplier), appears quite modest. Considering this fact, it's no use trying to squeeze an exorbitant FSB frequency in a system, that will be aimed mainly at running office applications.

As we change the type of the applications, the situation alters drastically. Content-creating applications, which are used in this test, require huge memory resources, so the influence exerted by L2 cache comes to naught, while the memory bus bandwidth comes in the forefront. As a result, Duron CPU with 154MHz FSB becomes the leader and overtakes both the elder Athlon with 100MHz FSB and Pentium III.

The situation with SYSmark 2000 is practically the same as we saw in the first round with Business Winstone 2001. No wonder, because the applications in SYSmark 2000 run in successions make the fastness and the architecture of L2 cache matter most of all.

We have also paid attention to the professional 3D Studio MAX. But this time we took the fourth version of this software instead of the formerly used third version. To assess the performance of the processors, we checked how long it took to render the Anisotropic Wheel scene at the resolution of 800x600. Naturally, the shortest time stands for the best result.

Since the rendering process involves the processor FPU, in SYSmark MAX Athlon and Duron perform much better than Pentium III, which FPU is not so fast. Speaking about Duron, its 133MHz bus gives it all chances to beat Pentium III in performance.

To test the systems archiving capabilities, we gauged the time they needed to compress a directory with all Unreal Tournament files. As in the previous case, the less is the time, the better is the result. As you can see on the chart, even Duron CPU with 154MHz FSB lags far behind its competitors. Most probably, it's for the small L2 cache again.

According to the results of this popular benchmark run at a low resolution Duron with 154MHz FSB surpasses not only Pentium III, but also the Athlon CPU with 100MHz FSB. Its success is determined by the memory bus, which works in this system at an over-nominal frequency alongside with the CPU bus.

As the resolution grows, 3DMark2000 indicates the leadership of Pentium III.

We used to state it before that Quake3 Arena is a gaming engine, where the performance strongly depends on the memory bus bandwidth. That's why there should be no surprise about Duron with 154FSB, which is the king of the hill.

The growth of the resolution in Quake3 Arena doesn't tell on the situation in general, though the performance gap between different systems got reduced significantly because of the limitations, imposed by the graphics memory.

Quake3: Team Arena is based on Quake3, but it operates more complicated geometry. In this game Pentium III is dogged even by Duron with 133MHz FSB.

However, the situation comes closer to the common Quake3 Arena as the resolution gets higher.

In Unreal Tournament the Duron CPU with 154MHz FSB is again ahead of both the similarly clocked Pentium III and Athlon with 100MHz FSB.

Nothing changes at the resolution of 1024x768x32. That's the specifics of the game, where the bottleneck is represented not by the graphics subsystem, but by the memory and CPU buses.

MDK2 is a bit easier for the CPU, since it doesn't strain the processor's computing capacities so much. Nevertheless, the results are a complete distress for Pentium III. It is only Duron with 100MHz FSB, which performance plunges deeper.

We can observe the same thing at higher resolutions.

This is one of the most up-to-date games, which uses utterly huge textures. So, once more the key figures are AGP and memory bus bandwidths. Consequently, no one is surprised to see the overclocked bus in AMD Duron system yield adequately good results again.

Once again resolution growth practically doesn't tell on the results.

Conclusion

We have witnessed the triumph of AMD Duron as an ideal CPU for overclockers, although it was a well-known fact already. This CPU has pleasantly low price and often reaches the height of 1GHz during proper overclocking. If used on mainboards supporting 133MHz FSB, Duron may be regarded as a serious rival even for Pentium III. As our tests have shown, in most 3D games 1GHz Duron-based systems with an overclocked FSB prove to be faster than similar systems built on Pentium III. There should follow a remark that in office applications Pentium III finally resists Duron's aggression. Anyway, the performance in business applications is not that crucial for an overclocker as fps rates in games.

If you don't approve of extreme overclocking, you may enjoy a really good performance gain if you only set your Duron at 133MHz FSB. Thanks to the synchronously working memory and CPU buses, Duron processor with 133MHz FSB frequency nearly catches up with Athlon, which works with 100MHz FSB.

As a final word, we should admit that nowadays the combination of AMD Duron CPU and a mainboard based on VIA KT133A chipset is the best for an overclocker, who strives to have high performance for small money.