Underclocking is far more likely to be an issue for the board than the CPU. So long as the board has dividers for the PCI/AGP/ISA busses to keep them close to spec when at 66MHz FSB, the CPU shouldn’t care.

My DFI board could in theory run a 60MHz bus.

So you think if the 500Mhz CPU can run on 66Mhz then there shouldnt be any issue with any of these other CPUs even though its not listed in their specs (on wiki)? But why is it then listed there in the first place... or is it just a manufacturer thing, saying that "they are inteded for 100Mhz" or something like that?

AMD K6-III and K6plus CPU runs fine at 66 MHz FSB as long as it POST correctly and have the necessary core voltage options.

On K6plus CPUs, the multiplier can be changed on the fly thru SetMul ranging from 2.0x to 6.0x, with the exception of 2.5x.

Alright, thank you! Interesting case with 2.5x though. Guess its due to only having 1.0 increments?

I tested K6-3+ (modded K6-2+) with 50 MHz bus (and much more) some time ago. I didn't notice any issues with 50 MHz but it was not useful. Here are the results.

Kordanor wrote on 2023-09-26, 14:32:

According to the Wiki thats not possible.

Wow, really? And what tells about this matter the universal knowledge of g00gl? 😁 😁 😁

Seriously, wikip...a is full of bu...hit. I've successfully tested mine K6-2+/500 down to 200 MHz (3 x 66 MHz FSB) on PCChips socket 7 mobo (I do not have any ss7 board) and the CPU worked just fine.

Google told me even less. Most pages only list 100 Mhz 😁
If I didnt see the Video from Phil I would not have known in the first place 😁
But its great to know, thanks a lot!

Kordanor wrote on 2023-09-26, 15:01:

Guess its due to only having 1.0 increments?

The increments are 0.5x and being unable to set 2.5x thru software is just a limitation of the K6plus microarchitecture.

analog_programmer wrote on 2023-09-26, 16:30:

Wow, really? And what tells about this matter the universal knowledge of g00gl? 😁 😁 😁

Seriously, wikip...a is full of bu...hit. I've successfully tested mine K6-2+/500 down to 200 MHz (3 x 66 MHz FSB) on PCChips socket 7 mobo (I do not have any ss7 board) and the CPU worked just fine.

That Wikipedia article was written by clueless people who didn't do some actual research and followed the things "by the book". 🤣

Kordanor wrote on 2023-09-26, 16:43:

Google told me even less. Most pages only list 100 Mhz 😁

I'm assuming it will run fine at 2 x 50 MHz FSB, I just haven't bothered to test it lower than 200 MHz.

analog_programmer wrote on 2023-09-26, 17:02:

Kordanor wrote on 2023-09-26, 16:43:

Google told me even less. Most pages only list 100 Mhz 😁

I'm assuming it will run fine at 2 x 50 MHz FSB, I just haven't bothered to test it lower than 200 MHz.

There is SpeedSys screenshot of a K6-2+ running at 2x60MHz here, on page 1:
SetMul - Multiplier control for VIA C3 / AMD K6+7+8 Mobile / Cyrix 5x86
I do not have a motherboard with 50MHz FSB option to try. But 60MHz FSB is never a problem with any Socket 7 CPU.

Cool, thanks. Yeah, no need for 50Mhz anyways. If I can do 66Mhz that would be good enough (at 2x or 2.5x)