Can It Be Done?
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Since the introduction of the K6-III processor, there have been many questions about which motherboards will support it. AMD does maintain a list of ‘officially supported’ motherboards, however this does not mean that you cannot use the K6-III if your board is not on that list. AMD is very conservative about which boards they list, due to liability issues. They use several criteria in their determination, including core voltage, bus speed, CPU multiplier and the maximum amperage the motherboard can handle. For the K6-III, this means a 2.4v vCore, 100MHz bus speed, 4.0x and higher multiplier and at least the ability to handle the maximum current the processor may draw. For the amperage requirement, AMD actually tests well beyond the maximum that the processor may draw just for a ‘buffer’. For example, to make the list for the K6-III 450 the motherboard must handle at least 16A. For more information on official electrical specifications for most processors, see our CPU Power Requirements article.
Though most ‘older’ motherboards do not have a 2.4v setting in the documenations, there are a number of them that actually can provide this using ‘undocumented’ settings. Some manufacturers have provided this information on their websites, and we have a partial list in our How To: Older Motherboards with <2.5v vCore Support article. While motherboards manufactured in the last two years will have 1.5x to 5.5x multipliers, some are limited to 3.5x, as are those older than two years. Fortunately, the K6-III interprets the 2.0x multiplier as 6.0x – perfect for running at either 400MHz (6.0 x 66MHz) or even 450MHz (6.0 x 75MHz). As most everyone recognizes today, if the processor was designed to handle a 100MHz bus, it can certainly handle 66MHz or 75MHz (83MHz bus speed is not recommended for any motherboard that does not have async or pseudo-sync PCI).
One issue that should be considered is whether the motherboard uses linear or switching voltage regulators. Linear regulators dissipate quite a bit of heat during operation, and therefore could cause some problems if the current gets close to the specified maximum. Switching regulators do not have this problem. It is also important to understand that the processor data sheets specify both ‘typical’ and ‘maximum’ power dissipation, and therefore current draw. The conditions under which the maximum power will be dissipated is not specified, but presumably it is achieved when the processor is being used to its maximum potential – which is extremely rare. This does not mean, however, that you should rely on the ‘typical’ power figure to determine if your board will support that processor.
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