Hi,

As far as I remember and trying to confirm it with internet searches most sites also agrees that Socket 3 officially topped at 50Mhz FSB, in fact searching theretroweb.com for Socket 3 motherboards supporting 55Mhz returns zero MBs officially supporting it.

If you really need 55Mhz FSB, you might try overclocking one of the 50Mhz FSB MBs to 55Mhz, it is a 10% OC, so it is in the doable but not guaranteed to work or necessarily easy category, note that Socket 3 motherboards, if they have PCI slots, also often derives the PCI bus frequency from the FSB, and VLB cards are also tied to it, so you might also OC the PCI and VLB cards and not only the MB and CPU in this case.

I will put this topic on watch because I'm interested if motherboards officially supporting this frequency exists, but I think if they exist they are not common.

MagefromAntares wrote on 2026-06-26, 09:08:

Hi, […]
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Hi,

As far as I remember and trying to confirm it with internet searches most sites also agrees that Socket 3 officially topped at 50Mhz FSB, in fact searching theretroweb.com for Socket 3 motherboards supporting 55Mhz returns zero MBs officially supporting it.

If you really need 55Mhz FSB, you might try overclocking one of the 50Mhz FSB MBs to 55Mhz, it is a 10% OC, so it is in the doable but not guaranteed to work or necessarily easy category, note that Socket 3 motherboards, if they have PCI slots, also often derives the PCI bus frequency from the FSB, and VLB cards are also tied to it, so you might also OC the PCI and VLB cards and not only the MB and CPU in this case.

I will put this topic on watch because I'm interested if motherboards officially supporting this frequency exists, but I think if they exist they are not common.

Thank's for your explanation!

I have a luckystar ls-486e rev C2 that supports 55fsb. and is also working. I was just wondering if there are more motherboards that support it 😀

IIRC, the later pages in this mega thread 3 (+3 more) retro battle stations mentions some boards which are even 66 MHz capable ...

H3nrik V! wrote on 2026-06-26, 10:35:

IIRC, the later pages in this mega thread 3 (+3 more) retro battle stations mentions some boards which are even 66 MHz capable ...

Wow, actually this is more than I expected 😀, however the exact 55Mhz FSB still seem to be relatively rare, checking out the specs for some of these MBs most of them skipped 55Mhz and went straight to 60 Mhz or 66 Mhz.

Thinking about it, the 66Mhz FSB actually makes a lot of sense, 33Mhz is the standard PCI frequency and instead of having a circuit for the PCI bus clock they could simply halve the FSB frequency.

MagefromAntares wrote on 2026-06-26, 10:56:

H3nrik V! wrote on 2026-06-26, 10:35:

IIRC, the later pages in this mega thread 3 (+3 more) retro battle stations mentions some boards which are even 66 MHz capable ...

Wow, actually this is more than I expected 😀, however the exact 55Mhz FSB still seem to be relatively rare, checking out the specs for some of these MBs most of them skipped 55Mhz and went straight to 60 Mhz or 66 Mhz.

Thinking about it, the 66Mhz FSB actually makes a lot of sense, 33Mhz is the standard PCI frequency and instead of having a circuit for the PCI bus clock they could simply halve the FSB frequency.

It has to do with the cost and type of commodity crystal oscillators that became available on the market.

Generally any crystal oscillator that has 55mhz will also have 60mhz.

This is because of the existence of the Cyrix 6x86-pr133 which used 55mhz FSB.

Obviously no 486 used that bus but later 486 boards might include it because crystal oscillators were being built to support pentium boards of the time.

Depending on how many pins and jumpers the oscillator block required many 486 makers would attempt to choose simpler oscillators with fewer speed selections but later on it was usually cheaper to get what was on offer.

The luckystar ls-486e rev:c2 on 4x55 fsb.