Motherboards Supporting Increased Bus Frequency

When considering overclocking problems, keep in mind that one of the main over-clocking aims is to improve the performance of legacy computers without significant financial investment. In many cases, the hardware configuration of such computers includes components whose parameters can't exactly be called modern or promising. However, such legacy systems still exist, and, what's more, adequately serve their users' purposes.

The following table contains a list of motherboards for Pentium processors. These motherboards support non-standard host bus frequency values of 75 and 83 MHz. This data may help you in choosing the optimum mode for overclocking the computer components.

The first column lists motherboard manufacturers; the second column specifies the name of the board. The remaining three columns contain the version number (X.X+ means X.X and higher) and recommended jumper positions for the corresponding bus frequency. Settings for the jumpers that specify bus frequency are listed in ascending order according to their respective numbers: 0 means open, 1 means short, combinations like 1-2 or 2-3 mean numbers of pins to be connected by jumper. Before you start overclocking, make sure that you have carefully studied the motherboard manual. The values shown in the table presented here should only be considered as an example illustrating overclocking methods. Note that the data provided in the table may not correspond exactly to your motherboard, as manufacturers of specific motherboards may introduce some changes into its design without notification. It is therefore strongly recommended that you check this data before overclocking and make sure that this information is consistent with the instructions provided in the motherboard manual. This is the only way to avoid regrettable mistakes. Some of this material, along with updated information, can be found on the Internet at the addresses www.sysopt.com/mb83mhz.html and www.sysopt.com/mb100mhz.html.

The next table lists certain parameters of popular motherboards that provide for high performance of the CPU, and therefore, improve overall system performance.

There are a few words to be said concerning the choice of a modern motherboard that is intended for use in overclocking modes.

Contemporary motherboards have a wide range of supported bus frequency values. However, if you were to compare motherboards according to this aspect only, you would notice that different boards vary not only by their supported bus frequency values, but also by their distribution within the frequency range. Usually, the supported values are not distributed evenly, but rather are grouped around a few areas within the entire range. This is due to the fact that the architecture of these newer motherboards uses different frequency synthesizer chips. This may affect the choice of the motherboard best suited for processor overclocking. Usually, brand name boards like Abit and ASUSTeK are very good for overclocking. These could be, for instance, the Abit BX6 Rev. 2.0 or the ASUS P2B Rev. 1.10. Both of these boards are noted for their support of a relatively large number of processor bus frequencies. However, most of the optimum overclocking frequencies provided by Abit BX6 Rev.2.0 are concentrated in the 112-133 MHz range, while the best over-clocking frequencies provided by ASUS P2B Rev.1.10 are grouped within the 100-124 MHz range. This grouping of supported frequencies influences the fields of optimum application for each motherboard. For example, when overclocking Celeron processors intended for the bus frequency of 66 MHz, the best results can be achieved when using ASUS P2B Rev. 1.10 motherboards, since they provide you with the ability to gradually increase the bus frequency within the range of 100-124 MHz. If you are going to overclock a Pentium II, consider the fact that all Pentium II processors intended for a bus frequency of 100 MHz usually run reliably at a frequency of 112 MHz. Because of this, motherboards like Abit BX6 Rev. 2.0 are of particular interest for this case. These motherboards allow you to set the maximum bus frequency (higher than the usual 112-115 MHz), because it allows you to gradually increase the bus frequency in the range of 100-124 MHz.

As was mentioned earlier, CPU stability at high processor bus frequencies can be achieved by increasing the voltage supplied to the processor. If there are no built-in tools for voltage tweaking, you can accomplish this task using insulating varnish or adhesive tape according to the directions given in Chapter 13. This is possible with practically all modern motherboards.

Note that currently, support for processor bus frequencies above 150 MHz is not necessarily a crucial advantage that plays a decisive role when choosing a motherboard, despite that for the moment there are certain motherboards on the market that are advertised as supporting bus frequencies up to 200 MHz. This is due to the fact that for the moment it is still difficult to find hardware components for such motherboards - memory modules, for example - that would tolerate such high frequencies. Besides, the Celeron and Pentium II processors intended for standard bus frequencies of 66 and 100 MHz, respectively, don't allow such a drastic increase in their external frequencies. Not even all representatives of the Pentium III family support such a high values for the processor bus frequency. For example, not all specimens of Pentium III with the Coppermine core, intended for use at an FSB frequency of 100 MHz and allowing relatively high values of the bus frequency will be stable and reliable at FSB frequencies approaching 150 MHz. The only exception is the Pentium III that is rated to run at an FSB frequency of 133 MHz. For such processors, the bus frequency of 150 MHz is of specific interest, but again, as usual, only for the first representatives of this line.

However, when estimating the possibility of using one of these increased bus fre-quencies supported by your motherboard, you should also consider the fact that the AGP and PCI bus frequencies are determined by the FSB frequency. Bus frequency values set for these buses depend on the motherboard architecture and on the functional capabilities of their chipsets. If extremely high frequencies are set for these buses, it may lead to the malfunctioning or failure of the components connected to them, for example, DIMM SDRAM modules, video adapters (AGP or PCI), hard drives, etc.

Now let us discuss some specific features of the motherboards that support high processor bus frequencies.

Many motherboard manufacturers advertise new technologies used in the architecture of their product. This advertising is often a bit misleading, because technologies proclaimed as "new" may have been in use for a while before manufacturers felt that they were sure of its reliability. Consider, for example, the SoftMenu technology, which allows you to set and manage overclocking modes via BIOS Setup. This technology is widely advertised by Abit, but has been in use in QDI motherboards for a relatively long time. You should also understand that all of these innovations are based on the specifications and the architecture of modern processors. For instance, choosing the motherboard name Chaintech 6BTM from the Overclocker BIOS menu allows you to control external processor frequencies using SoftMenu. However, there is still a switch on the motherboard itself that assigns the Sel 66/100# amplitude levels and that in a normal mode sets the external frequency. At the same time, the actual frequency the processor uses is chosen in BIOS Setup. After setting the JP7 Sel66/100# level to Low, that is, to 66 MHz, the processor that is used to running on 100 MHz "frees" the multiplier. As a result, you gain the opportunity to set any external frequency and any multiplier you want in BIOS Setup. In many cases, this will allow you to get around the problem of locked multipliers. This technique is described at www.ixbt.com and has been tested on the Chaintech 6BTM motherboard. You might also try it with other motherboards that allow users to set the external frequency both in BIOS Setup and by switches.