KIng Mustard wrote on 2025-12-14, 12:32:

I recently bought a PC containing an Intel Pentium MMX 166 overclocked to 225 MHz. I am wishing to upgrade this CPU. […]
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I recently bought a PC containing an Intel Pentium MMX 166 overclocked to 225 MHz. I am wishing to upgrade this CPU.

There are no markings on the motherboard (that I can see) but it is likely a Matsonic MS6260 or Jetway J-542B/C(S) motherboard that I have.

It has the ALi Aladdin V M1542 chipset with M1543C Southbridge. The BIOS is v4.51PG V.542C/542CS D06 (25 Oct 2000).

I believe my best options are AMD K6-2 and AMD K6-III CPUs.

Assuming this is the case, having done a brief look on eBay, it appears my options based on current listings would be:

AMD K6-2 300 MHz (£14)
AMD K6-2 350 MHz (£13)
AMD K6-2 400 MHz (£15)
AMD K6-2 450 MHz (£25)
AMD K6-2 475 MHz (£48)
AMD K6-2 500 MHz (£22)
AMD K6-2 533 MHz (£35)
AMD K6-2 550 MHz (£90)

There were currently no reasonably-priced AMD K6-III CPUs on there.

That AMD K6-2 550 MHz CPU is a bit too expensive, in my opinion (£90).

Would you say that AMD K6-2 533 MHz (£35) is a good purchase/middleground?

Is eBay even my best place to look?

https://www.cpu-world.com/CPUs/K6-2/TYPE-K6-2.html

As noted, OC it to 100 MHz FSB.

Looks good to me. Maybe a more experienced user will correct me.

Hi KIng Mustard,

Seeing that this board runs the D06 BIOS for the 542C/542CS, it probably is a Jetway J-542C(S) board. I have this board, running a K6-III+/450 at 500MHz.

Yes, the D06 BIOS fully supports the AMD K6-2+ and K6-III+ CPUs as well. I believe the sweet spot for this board is the K6-2+/570 that can run 600MHz without a sweat.
So if you can find one of those for a reasonable price…

If not, I agree with @Nexxen that the K6-2/533 is a nice choice for this board and can be overclocked to 550MHz in most cases. But for some you may need to up the Vcore one notch from 2.2V to 2.3V.

Note that, for some reason, the BIOSes for the Jetway 542B(S) and 542C(S) don’t support AMD’s Write-Allocation feature. So any K6 model will be underperforming a bit.
Intel CPUs don’t have this feature but AMDs K5/K6 do, and when enabled gain about 10% performance.

I have patched the D06 BIOSes for both the J-542B(S) and J-542C(S) boards to enable this WA feature for all K6 models. So whatever K6 CPU you choose, you may want to run the patched BIOS for optimal performance. You can download these patched BIOSes from my “The Unofficial K6-2+/K6-III+ page”.
The link is in my signature below.

Cheers, Jan

Chkcpu wrote on 2025-12-15, 15:22:

I believe the sweet spot for this board is the K6-2+/570 that can run 600MHz without a sweat.

These used to be on ebay from a seller with thousands available, but I don't see the listing right now.

I think any "plus" CPU is the way to go, particularly when a suitable BIOS is available. These were usually sold as mobile CPUs and overclock well in a desktop. For example, I got a few 400MHz/1.6v rated chips that all work fine at 550MHz/2v, and they all converted successfully to the 3+ mode with full cache (...the built in L2 cache can make a big difference in some cases).

I would pick:
AMD K6-2 400 MHz (£15)

The K6-2 doesn't scale as well much past 400MHz due to L2 Cache speed/FSB etc. If it was a K6-2/3+ then it would do better.

If you find a 570 2+ you can mod it to 3+ 😀

bought my K6-2+ from Ali Express at u$s 29 about a year ago and since then it almost doubled the price

https://es.aliexpress.com/item/10050045778778 … ayAdapt=glo2esp

got it oced to 600Mhz rock stable.

Probably not a bad price for a 550 2+

The 570 2+ are more common

Living wrote on 2025-12-16, 02:05:

bought my K6-2+ from Ali Express at u$s 29 about a year ago and since then it almost doubled the price

https://es.aliexpress.com/item/10050045778778 … ayAdapt=glo2esp

got it oced to 600Mhz rock stable.

I got mine from the same seller last year (USD$29.60), unfortunately mine is unstable at 600 even when overvolted. But 550 is still good honestly.

NeoG_ wrote on 2025-12-16, 09:17:

Living wrote on 2025-12-16, 02:05:

bought my K6-2+ from Ali Express at u$s 29 about a year ago and since then it almost doubled the price

https://es.aliexpress.com/item/10050045778778 … ayAdapt=glo2esp

got it oced to 600Mhz rock stable.

I got mine from the same seller last year (USD$29.60), unfortunately mine is unstable at 600 even when overvolted. But 550 is still good honestly.

Surprising that you can’t get 600mhz.

Try a board recap, and bios update. (I know conventional wisdom says bios update won’t help cpu stability, but I have seen it help before multiple times.)

Also be sure the instability isn’t related to another factor. Like maybe fsb instability what setting you are trying for 600. Are you using 100fsb for 550 and 600 or some oddball like 92 and 110

Sphere478 wrote:

Surprising that you can’t get 600mhz.

Try a board recap, and bios update. (I know conventional wisdom says bios update won’t help cpu stability, but I have seen it help before multiple times.)

Also be sure the instability isn’t related to another factor. Like maybe fsb instability what setting you are trying for 600. Are you using 100fsb for 550 and 600 or some oddball like 92 and 110

Yeah it’s a bit weird. 100x5.5 and 100x6, latest bios. At 600 the CPU starts fine but once it warms up the FPU starts acting funny. After 10-20 minutes in GLQuake the geometry starts acting up - walls and objects start shifting around slightly and over 5mins it gets worse then freezes.

For a while I thought the Voodoo3 was kaput but then I remembered that there’s no hardware TnL so the geometry is being calculated on the CPU, putting it back to the stock 550 speed fixed it.

Since you are in Europe, there is a guy selling K6-3+ in Germany for 15 EUR, outstanding deal:

https://www.ebay.com/itm/406334987280?_skw=k6 … %3ABFBM-Mft7eZm

This will overclock to 550-600Mhz easily

Pino wrote on 2025-12-19, 13:49:

Since you are in Europe, there is a guy selling K6-3+ in Germany for 15 EUR, outstanding deal:

https://www.ebay.com/itm/406334987280?_skw=k6 … %3ABFBM-Mft7eZm

This will overclock to 550-600Mhz easily

He's in Germany but not shipping to anywhere in Europe. That - combined with the unfeasibly low price - is highly suspicious...

dionb wrote on 2025-12-19, 16:48:

He's in Germany but not shipping to anywhere in Europe. That - combined with the unfeasibly low price - is highly suspicious...

Humm, yeah that is suspicious, it says it ships to US, but then shipping would be double the price of the CPU itself, so not worth it.

dionb wrote on 2025-12-19, 16:48:

He's in Germany but not shipping to anywhere in Europe. That - combined with the unfeasibly low price - is highly suspicious...

The shipping is an artifact of how ebay works - If you go to ebay.de and then manually set the post region to deutschland the postage is 2.90 EUR for example

NeoG_ wrote on 2025-12-19, 23:54:

dionb wrote on 2025-12-19, 16:48:

He's in Germany but not shipping to anywhere in Europe. That - combined with the unfeasibly low price - is highly suspicious...

The shipping is an artifact of how ebay works - If you go to ebay.de and then manually set the post region to deutschland the postage is 2.90 EUR for example

Germany, yes- but elsewhere in Europe is explicitly denied:

Standort Obrigheim, Deutschland
Versand nach Weltweit
Ausgeschlossen Europa, Russische Föderation

OP's UK is sometimes unsure of whether it's in Europe or not, but for Ebay shipping rules it is, so UK is denied here too.

dionb wrote on 2025-12-20, 14:23:

NeoG_ wrote on 2025-12-19, 23:54:

dionb wrote on 2025-12-19, 16:48:

He's in Germany but not shipping to anywhere in Europe. That - combined with the unfeasibly low price - is highly suspicious...

The shipping is an artifact of how ebay works - If you go to ebay.de and then manually set the post region to deutschland the postage is 2.90 EUR for example

Germany, yes- but elsewhere in Europe is explicitly denied:

I sent him a message and he does ship at least to The Netherlands. But shipping cost would be 30 Euros. To inflated IMO so I won't order one.

I would choose that AMD K6-2 533 MHz (£35), but i don't know if results better trying to get a K6 iii.