Hi,

This is very curious indeed, and I can only come to three conclusions:
1. The motherboard for some reason is hard wired to provide the MMX dual voltages and that could cause problems with some non MMX CPUs.
2. The sticker is not telling the truth.
3. It would be extremely weird, but for some incomprehensible reason the BIOS might use MMX instructions. (I have no idea why would you do that however)

I never previously encountered a Socket 7 motherboard which was explicitly only supported MMX CPUs, so I'm also very interested where this will go. Thanks for sharing this.

Weird indeed, considering the Marl is 430HX based and thus doesn't officially support P55C IIRC 🤔

BitWrangler wrote on 2026-05-10, 13:48:

Hi gang, […]
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Hi gang,

I am trying to figure out all there is to know about this piece of ... hardware. It was purchased long ago at scrap price and has been a little banged around. That's not a burn on the socket, it's cola or coffee or something.

It looks likely to have issues, but I am trying to find out what the heck is going on with that MMX only sticker before I start messing, as I might end up chasing my tail while trying to fix it, if I don't know for sure it still supports P54C and not P55 split plane.

From looks it only has single plane voltage, it looks identical to every other Marl picture I can dredge up.

Now I would have thought maybe the sticker was a used part reseller who put it on to stop his customers jamming an s370 in there, but the model sticker on top seems to be in similar typeface and has MMX in the name. I don't know if it was just MMX ready for the overdrive implied due to BIOS upgrade, or it has some sneaky extra regulation I cannot for the life of me spot.

Anyone got any ideas what is going on?

Maybe one of these...https://groups.google.com/g/intel.motherboard … /m/epMcik0pbAsJ

See https://theretroweb.com/motherboards?manufact … =24&name=amazon

PC Hoarder Patrol wrote on 2026-05-10, 16:33:

BitWrangler wrote on 2026-05-10, 13:48:

Hi gang, […]
Show full quote

Hi gang,

I am trying to figure out all there is to know about this piece of ... hardware. It was purchased long ago at scrap price and has been a little banged around. That's not a burn on the socket, it's cola or coffee or something.

It looks likely to have issues, but I am trying to find out what the heck is going on with that MMX only sticker before I start messing, as I might end up chasing my tail while trying to fix it, if I don't know for sure it still supports P54C and not P55 split plane.

From looks it only has single plane voltage, it looks identical to every other Marl picture I can dredge up.

Now I would have thought maybe the sticker was a used part reseller who put it on to stop his customers jamming an s370 in there, but the model sticker on top seems to be in similar typeface and has MMX in the name. I don't know if it was just MMX ready for the overdrive implied due to BIOS upgrade, or it has some sneaky extra regulation I cannot for the life of me spot.

Anyone got any ideas what is going on?

Maybe one of these...https://groups.google.com/g/intel.motherboard … /m/epMcik0pbAsJ

See https://theretroweb.com/motherboards?manufact … =24&name=amazon

Thanks very much, I got there before you updated via the MkII amazon clue at http://cwcyrix.nsupdate.info/intel-legacy-fil … /Desktop/1990s/

So some inaccuracies on that retroweb page, as looking at the elhvb link with the capture of the trigem info, it clearly states in the history section that the Amazon II is the P54 version and the Amazon III is the MMX version. Therefore it seems that the pic on the Amazon 3 page is actually an Amazon 2, since it has a P54 in it.

Some unanswered questions still though, like how come I seem to have 512kb of cache when all versions got downgraded to 256 in earlier 1997 according to one reference and by chip dates this seems to be a Q4-97 board. However, since info is all over the place on this IDK if that's gonna be all that correct. Secondly I forgot there's a "Made in Canada" sticker on the bottom of the darned thing. Which seems off if it's Trigem made in Korea? Taiwan?. The font on the stickers reminds me of Seanix, what their labels look like. So wondering if they some how crosslicenced Marl with Trigem mods and assembled here, or it got a Made in Canada for the system rather than the motherboard.

Also back in ancient times I seem to have pencilled BCM SQ598 onto it. IDK if I should trust myself, references online were poor 2 plus decades back, might have got it from total hardware 99. I think it was pre-Stason and soggi might have been around then but only had a dozen boards listed. It is possible I got it out of original motherboards.org or sysopt.com sources like those that got scraped before doomsday onto elhvb. Can't see if BCM had Canadian operations at the moment, they seem to be a big intel partner though.

So while Amazon 3 seems best fit, still kinda doubtful about who made it. But yes it seems like it really was an MMX only board. Must be rawdogging the 3.3V straight off the PSU for i/o side.

The problem with that now is that I haven't got an MMX I want to kill... erm, test with. Amazon 3 only seems qualified to P200MMX 15.7W and the P233 is 17Watts, so even K6-166 at 17W might blow the reg. Though theoretically, on lower FSB than 66 it won't hit 17W. Does not tell me much about whether it's worth obtaining it's own MMX for though running it in cripple mode. Might have to de-sink the regulator and look up specs independently to see if there is wiggle room.

Edit: retroweb search is a bit weird though ain't it, yesterday or saturday I was searching 430HX on ATX to look for alternate part numbers but I swear those Trigems didn't pop up then.

I think the sticker doesn't mean anything. The board was probably snatched from a Pentium MMX system and the sticker was there just to point out redundancy of trying to switch CPU to the regular Pentium.

MagefromAntares wrote on 2026-05-10, 14:24:

1. The motherboard for some reason is hard wired to provide the MMX dual voltages and that could cause problems with some non MMX CPUs.

There is no dual voltage on Intel ATX boards.

Anyway. I realised it was pretty stupid that I don't have an Intel Pentium MMX tester. Got two installed CPU, one in a chassis with fragile plastics I hate opening, and one in a proprietary form factor buried under 500 screws and bits of metal to get to it. So I don't like getting into either unnecessarily, plus I still want them to work when I am done, so they can stay there for best chance of that.

Shook some local trees, nothing fell out, went onto eBay, 🤣 kinda sparse there now, I thought there would still be thousands coming from Chinese CPU guys but nope. It was looking like I'd have to fork $50ish all in for one, item and shipping, maybe more if tariffs involved, plus the UPS classic "We filed the customs paperwork for you, wrongly, so now you are taxed on $500 value and we want $50 for providing this service." ... continually have the battle "don't send it UPS, don't send it UPS, whatever they say, don't send it UPS" and seller is like "okay" then it shows as shipped with a UPS tracking and seller is like "Well it was $5 cheaper and they SAID it was all inclusive" so screw all that noise for anything less than unicorn.

So I went with an option that gets me two for $50 with free shipping. I'll tell you all exactly when they arrive and get eyeballed, no point if they're pin ravaged scrap. May only be an option for Canadians.

It is a reliable storefront methinks for other stuff, but in pics they have SL293 and in text description it says SL27S ... so either/or or mix and match I guess. Whatever, one tester, one spare to swap around and cherry pick the overclocker to play with.

The Serpent Rider wrote on 2026-05-10, 19:36:

I think the sticker doesn't mean anything. The board was probably snatched from a Pentium MMX system and the sticker was there just to point out redundancy of trying to switch CPU to the regular Pentium.

MagefromAntares wrote on 2026-05-10, 14:24:

1. The motherboard for some reason is hard wired to provide the MMX dual voltages and that could cause problems with some non MMX CPUs.

There is no dual voltage on Intel ATX boards.

I think this post contradicts itself, if the board is snatched from a Pentium MMX system it has to have dual voltages https://www.cpu-world.com/CPUs/Pentium/TYPE-P … tium%20MMX.html

3.3V input/output level and 2.8V core.

And this is exactly why the MMX only sticker is interesting because this motherboard doesn't supposed to have that, but it needs the dual voltages for a MMX to function properly.

This suggestion from me is that for some reason they had to modify a regular Pentium board for dual voltage usage so they can use the MMX processors instead of the regular ones.

EDIT: Also check the pinout and the 3.3 DC Specifications chapter of the Intel MMX Datasheet https://datasheet.octopart.com/PENTIUM-MMX-23 … eet-7279168.pdf

MagefromAntares wrote on 2026-05-10, 22:27:

And this is exactly why the MMX only sticker is interesting because this motherboard doesn't supposed to have that, but it needs the dual voltages for a MMX to function properly.

It has a 2.8V voltage reg and takes 3.3V from the ATX supply.

jmarsh wrote on 2026-05-11, 00:05:

MagefromAntares wrote on 2026-05-10, 22:27:

And this is exactly why the MMX only sticker is interesting because this motherboard doesn't supposed to have that, but it needs the dual voltages for a MMX to function properly.

It has a 2.8V voltage reg and takes 3.3V from the ATX supply.

Precisely, that is what I meant when I said dual voltages, the motherboard has to supply dual voltages to the CPU (In the Intel tech spec it can be seen that they not only have different voltages, but very different tolerances as well, so instead of a simple step down, it has a full separate power regulation for the dual voltages required by the CPU), it isn't the PSU that does it.

EDIT: Wikipedia, but the official definition is the same:https://en.wikipedia.org/wiki/CPU_core_voltag … ual-voltage_CPU

EDIT 2: I hate using Wikipedia for reference because it can be (except protected pages) edited by anyone at anytime, so there is the actual official document for the Pentium MMX mentioning dual voltages: https://download.intel.com/design/intarch/app … ts/27320602.pdf, yes it is for the embedded version there are some slight differences, but the concept is the same.

Dual voltage was a crutch for AT standard. This motherboard grabs +3.3v directly from ATX PSU, so no splitting from +5v rail happens. There's only one linear voltage regulator on the board.

The Serpent Rider wrote on 2026-05-11, 01:54:

Dual voltage was a crutch for AT standard. This motherboard grabs +3.3v directly from ATX PSU, so no splitting from +5v rail happens. There's only one linear voltage regulator on the board.

I think we miscommunicated 😀 I'm not speaking about the Dual Voltage from the PSU, I'm speaking about the Dual Voltage provided by the Motherboard to the CPU (According to the design document made by Intel I have linked).

Intel ATX motherboards do not provide anything outside of one linear regulator for CPU, that directly converts +5V rail to 2.8-3.45, depending on what you install. That's how it practically works for this board, everything else is just semantics.

The Serpent Rider wrote on 2026-05-11, 02:08:

Intel ATX motherboards do not provide anything outside of one linear regulator for CPU, that directly converts +5V rail to 2.8-3.45, depending on what you install.

Precisely, the motherboards need one regulator to provide the smaller voltage for the MMX core VCC, the 3.3 Volts for the I/O part of the chip can come from the PSU directly(and some filtering without needing a full regulator, to make it a bit more stable for the CPU), Intel calls this Dual Voltage in the document because it is a Dual Voltage for the processor, one of it comes from the regulator on the motherboard, another one from the PSU.

EDIT: Remember in my original post:

1. The motherboard for some reason is hard wired to provide the MMX dual voltages and that could cause problems with some non MMX CPUs.

I explicitly mentioned it as MMX dual voltages in an attempt to make it harder to confuse with the more general Dual Voltages term used in the domain of Motherboard Power Supplies

FWIW, I still have one my early-on Pentium class mainboards (Aopen AP5T). I know when I built it I put a bog standard Pentium133 in it (which I seem to still have in my CPU junkbox)

Now it's had a P200MMX in it for many years - I don't recall having to change any jumpers, but manual says it supports Pentium P54C and PP/MT (P55C)

Under "Setting CPU Voltage" it says to move a jumper, which changes Vcore:
3.45v = P54C
2.8v = (MMX P55C)

Further down in the same section it lists:
Intel P54C | Single Voltage | 3.45v
Intel MMC P55C | Dual Voltage | 2.8v

I don't see any mention of setting the second voltage for the "Dual Voltage" MMX

** It's still going strong - probably 20 years after I got it!

DaveDDS wrote on 2026-05-11, 04:31:

FWIW, I still have one my early-on Pentium class mainboards (Aopen AP5T). I know when I built it I put a bog standard Pentium133 […]
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FWIW, I still have one my early-on Pentium class mainboards (Aopen AP5T). I know when I built it I put a bog standard Pentium133 in it (which I seem to still have in my CPU junkbox)

Now it's had a P200MMX in it for many years - I don't recall having to change any jumpers, but manual says it supports Pentium P54C and PP/MT (P55C)

Under "Setting CPU Voltage" it says to move a jumper, which changes Vcore:
3.45v = P54C
2.8v = (MMX P55C)

Further down in the same section it lists:
Intel P54C | Single Voltage | 3.45v
Intel MMC P55C | Dual Voltage | 2.8v

I don't see any mention of setting the second voltage for the "Dual Voltage" MMX

** It's still going strong - probably 20 years after I got it!

Is this the board you've mentioned with the very compatible floppy controller for ImageDisk?
The reason there is no setting for the second voltage (which is Vio, in contrast to Vcore) is because it's always 3.3V (perhaps 3.45V on your board, close enough) even with an MMX CPU. That is, Vcore = Vio on the original Pentium, while they are two different voltages on the MMX, hence dual voltage.
As to whether you ever changed the jumper when switching to the MMX, I believe they're somewhat known for running overvolted indefinitely and not complaining.

jakethompson1 wrote on 2026-05-11, 04:36:

Is this the board you've mentioned with the very compatible floppy controller for ImageDisk?

Yes! - The reason I still have one is that when I first got one, and discovered how good the FDC was, I immediately bought another.

The reason there is no setting for the second voltage (which is Vio, in contrast to Vcore) is because it's always 3.3V (perhaps 3.45V on your board, close enough) even with an MMX CPU. That is, Vcore = Vio on the original Pentium, while they are two different voltages on the MMX, hence dual voltage.

That's pretty much what I figured.

As to whether you ever changed the jumper when switching to the MMX, I believe they're somewhat known for running overvolted indefinitely and not complaining.

I suppose I should check, but even if I hadn't set it - I'm not going to change it now! - the board has been working with the MMX for a long time without any incidents.

I had bought a batch of Omnitech p200mmx atx HX motherboard/cases decades ago from the tech colleges.

Sadly the 200mmx chips were gimped so they wouldn’t overclock and the boards lacked voltage control outside single voltage and dual voltage.

I would have liked to upgrade them to k6/k6-2 back in the day but they lacked the voltage needed and the bios update was nowhere to be found.

Somehow this thread did not catch my attention on earlier "marl" etc searches, but when I went looking for regulator information...
Intel AA-654850-206 Advanced/ML Marl motherboard lost VRM
Seems someone else turned up a board with a 2.8 capable VRM in it, but it is not clear if it was set up (with component values) to provide 2.8 or 3.3 .... given that there is a STD/VRE or OD/VRE jumper 3.3 to 3.45 I think, then the regular reg might have been the variable one. That board shown has a serial port not USB though, so not a Trigem for sure.

Further interesting info about yet another manufacturer, InBus engineering. (They seem only to supply a vanilla Advanced/ML which may be old stock or repro https://www.inbus.com/products/desktop/advanced_ml.htm ... or maybe "have supplied" that site looks decades old.

So the regulator is only 5 Amps... so yup, running at the ragged edge to go full 233 speed MMX on it. (It might work but if fan stalls, CPU draw plus no flow over reg fins might have it die)

The original plan in getting this board going was to represent a late 96 system with a P54C 166 in it, I ordered the 233 intending to set it at 2.5, but now I am seeing full regulator info I am tempted to fiddle the resistor to 3.3 and run the P54..... or I can put a trimpot in.

I wonder if there were any Marl boards with integrated radiator, which can be seen on late production Tuscon boards.