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xDavid Knell

The Strange Case of the K6-2/400
New life for old Socket 7 Boards

Stuck with an old motherboard that the manual says will only support up to a 233MHz processor?

You may be able to turbo it up to a roaring 400MHz (without even overclocking)!

That old standard (non-Super) Socket 7 motherboard you have may be capable of supporting a much more powerful CPU (processor) than you realised. Sure, the manual may say it can support a maximum of only 233MHz but the manual was printed long before more recent developments. In fact, using some of the later AMD processors like the K6-2/400 may nearly double that limit!

You know your Socket 7 dinosaur can support a bus speed of only 66.67MHz and that the multiplier has a maximum setting of, say, 3.5x. So how, you may ask, can it possibly support a 400MHz CPU?

The answer is that the K6-2/400 (and some of the other AMD CPUs as well) is a rather unusual animal. If you set the multiplier on the motherboard to multiply the bus speed by 2x, the K6-2/400 just smiles to itself (well, almost!) and multiplies the bus speed by 6x instead. And, as we all know, 6 x 66.67 (strictly 66 and two-thirds) MHz = 400MHz.

The fact that the K6-2/400 has this "remapped multiplier" capability is, of course, no accident. AMD deliberately designed it that way. Neither is the K6-2/400 alone. All CXT core K6-2 processors and all K6-III processors will interpret a 2x multiplier as 6x.

Before you get too excited though, you should be aware that your Socket 7 motherboard must meet the following criteria:

  • The BIOS must be able to at least recognise a standard AMD K6 processor

  • The motherboard must be able to support a dual-voltage MMX processor

  • The motherboard must be able to support a CPU core voltage of 2.2 - 2.4v (It is possible to run it at 2.5v but the chip will tend to overheat and extra cooling should be provided)

It is also worth bearing in mind that even if your motherboard meets the above criteria, there is a possibility that you still may not be successful. In particular, some motherboards with non-Intel chipsets have been reported as having problems.

Note: Even when the upgrade has been successful the BIOS may misreport the speed. It is advisable to use benchmark software (or a simple utility such as the "CPU Control Panel" mentioned at the bottom of this page) to check and measure the true speed of the chip. The erroneous information reported by the BIOS can then be ignored.


  1. Ensure your motherboard meets the criteria outlined above and that the BIOS is the newest version available.

  2. Switch off the computer and remove the cover, taking the usual precautions to guard against static electricity.

  3. Replace your present CPU with the AMD K6-2/400 (or an AMD CPU with similar capabilities, as mentioned above), making sure the chip is properly orientated in the ZIF socket.

  4. Make sure that the new AMD CPU has an adequate heatsink and fan. It is also recommended that thermal paste is used between the CPU and the heatsink to allow good heat transfer.

  5. Set the CPU core voltage to 2.2v by means of jumpers or dip switches on the motherboard. The settings are normally silkscreened on the motherboard, or see the motherboard manual.

  6. Make sure that the bus speed is set to 66.67MHz by means of jumpers or dip switches on the motherboard.

  7. Set the CPU multiplier to 2x, again by means of jumpers or dip switches as before.

  8. Replace the computer's cover and switch the computer back on.

Important Tip:

The BIOS on many of the older motherboards does not enable the "write allocation" feature of K6-2 processors. Without this feature enabled, writes to memory are very slow. However, there are several programs that can overcome this drawback; one of the best is a free utility called "CPU Control Panel" provided by PowerLeap.

The author of this article would like to thank CMonster for so kindly passing on the information.


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