Check out those red jumpers in the VRM socket next to the CPU. Have a look at this video, Necroware gives you a good understanding on how they work. You could also build one of his VRMs.

https://www.youtube.com/watch?v=CMiGVQbMC5U

RetroPCCupboard wrote on 2024-11-05, 11:20:

I bought this on ebay recently. […]
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I bought this on ebay recently.

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What caught my eye was that it was an AT board with built in Ps/2 socket and supports EDO RAM and Pentium MMX.

The seller posted a photo showing that they had it running a Pentium MMX (though at an odd frequency):

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The question though, is how did they set the voltages for the CPU? I can see no jumpers for it on the board. Presumably this is too early a board to support jumperless voltage setting?

I may be blind, but I can't see any identifying markings that might help me find a manual for it...

https://theretroweb.com/motherboards/s/pcchips-m520

PC Hoarder Patrol wrote on 2024-11-05, 11:31:

https://theretroweb.com/motherboards/s/pcchips-m520

Thanks! How did you identify it as this board?

This note on that website is a little scary:

Inadequate Power Delivery
This motherboard may have insufficient power delivery, which can lead to unstable or unsafe operation. In extreme cases, this may result in hardware damage, spontaneous combustion, or other electrical failures. Users should exercise caution and consider upgrading the motherboard power supply or other components to ensure safe and stable operation.

zuldan wrote on 2024-11-05, 11:25:

Check out those red jumpers in the VRM socket next to the CPU. Have a look at this video, Necroware gives you a good understanding on how they work. You could also build one of his VRMs.

https://www.youtube.com/watch?v=CMiGVQbMC5U

Fascinating. So it would seem that this motherboard doesn't support Pentium MMX and the seller most likely ran their MMX CPU at 3.3v instead of 2.8v. Obviously I don't want to kill my CPU, so won't be doing that! I will drop in a standard Pentium just to check the motherboard works OK. Then I guess I will have a project on my hands to make this work with an MMX CPU. A project for a later day though, as that sounds like a lot of work for an electronics novice like myself.

RetroPCCupboard wrote on 2024-11-05, 11:37:

Thanks! How did you identify it as this board? […]
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PC Hoarder Patrol wrote on 2024-11-05, 11:31:

https://theretroweb.com/motherboards/s/pcchips-m520

Thanks! How did you identify it as this board?

This note on that website is a little scary:

Inadequate Power Delivery
This motherboard may have insufficient power delivery, which can lead to unstable or unsafe operation. In extreme cases, this may result in hardware damage, spontaneous combustion, or other electrical failures. Users should exercise caution and consider upgrading the motherboard power supply or other components to ensure safe and stable operation.

An easy find using The Retro Web search page advanced options (socket, expansion slots, chipset etc.) - https://theretroweb.com/motherboards/

Loads on Vogons using the M520 successfully so don't worry too much about the power delivery note.

By the way, my hope for this platform is to make a Pentium MMX as slow as possible for compatability with older games. Hopefully the rather old chipset on this board will make it slower than can be achieved on a platform that officially supports the CPU. Hopefully it will be possible to be as slow as a fast 286 when combined with EDO ram on slow timings, an ISA video card and disabling caches and performance features of the MMX CPU. But, in the meantime, I do have a slightly more modern AT board that supports the MMX.

PC Hoarder Patrol wrote on 2024-11-05, 12:50:

An easy find using The Retro Web search page advanced options (socket, expansion slots, chipset etc.) - https://theretroweb.com/motherboards/

Loads on Vogons using the M520 successfully so don't worry too much about the power delivery note.

Ah. Handy. I didn't know you can search like that

It will be slower (although not very much) than the average VX boards because it doesn't have any L2 cache 😀
(until you'll find cache stick for it)

RetroPCCupboard wrote on 2024-11-05, 12:14:

zuldan wrote on 2024-11-05, 11:25:

Check out those red jumpers in the VRM socket next to the CPU. Have a look at this video, Necroware gives you a good understanding on how they work. You could also build one of his VRMs.

https://www.youtube.com/watch?v=CMiGVQbMC5U

Fascinating. So it would seem that this motherboard doesn't support Pentium MMX and the seller most likely ran their MMX CPU at 3.3v instead of 2.8v.

The BIOS supports it, but the board only has an onboard VRM for 3.3V, so you need to add the VRM to be in spec.

Add to that that the 5V-3.3V VRM is pretty notoriously bad/under-specced and it's not the best of boards to push your luck with.

If you really want to go with this classic piece of PC Chips crapware (which in itself is a good challenge), I'd follow suggestions for building your own VRM module for it, and then power that module directly from PSU and so actually reducing the load on the poor onboard components.

Obviously I don't want to kill my CPU, so won't be doing that!

Not likely, chances are that the MOSFET under the CPU socket will burn out at some point, but that will kill the motherboard, not the CPU. For that reason, old motherboards tend to be rarer than old CPUs to go in them.

I will drop in a standard Pentium just to check the motherboard works OK. Then I guess I will have a project on my hands to make this work with an MMX CPU. A project for a later day though, as that sounds like a lot of work for an electronics novice like myself.

Necroware's VRM is here:
https://github.com/necroware/s7-vrm

Note that it requires some SMD soldering (not trivial for a complete beginner) and draws power from the motherboard, so not perfect - but at least it draws 5V not 3.3V, so won't affect the underdimensioned VRM adversely.

RetroPCCupboard wrote on 2024-11-05, 12:54:

By the way, my hope for this platform is to make a Pentium MMX as slow as possible for compatability with older games. Hopefully the rather old chipset on this board will make it slower than can be achieved on a platform that officially supports the CPU. Hopefully it will be possible to be as slow as a fast 286 when combined with EDO ram on slow timings, an ISA video card and disabling caches and performance features of the MMX CPU. But, in the meantime, I do have a slightly more modern AT board that supports the MMX.

i430VX isn't a speed demon, but it's only a few percentage points behind the i430TX, which is Intel's fastest chipset for the MMX and clock-for-clock one of the fastest of the So7 chipsets overall. So choosing i430VX won't handicap it much. Not having L2 cache (like on this board...) will however handicap it significantly. Turning off L1 cache as well will get you seriously slow though.

If you wanted to choose the slowest chipsets for Pentium MMX, go for SiS 5511 with 6202 UMA graphics, or SiS5596 (same compontents integrated into the same chip). Not only does the integrated graphics eat half your memory bandwidth, you can also run on a single 32b SIMM, further halving the performance.

dionb wrote on 2024-11-05, 14:32:

The BIOS supports it, but the board only has an onboard VRM for 3.3V, so you need to add the VRM to be in spec.

Add to that that the 5V-3.3V VRM is pretty notoriously bad/under-specced and it's not the best of boards to push your luck with.

Well, to look at it another way, if you are going to experiment on something when you don't know what you are doing, then choose the crappiest thing you have to practice on 😀

dionb wrote on 2024-11-05, 14:32:

If you really want to go with this classic piece of PC Chips crapware (which in itself is a good challenge), I'd follow suggesti […]
Show full quote

If you really want to go with this classic piece of PC Chips crapware (which in itself is a good challenge), I'd follow suggestions for building your own VRM module for it, and then power that module directly from PSU and so actually reducing the load on the poor onboard components.

Necroware's VRM is here:
https://github.com/necroware/s7-vrm

Note that it requires some SMD soldering (not trivial for a complete beginner) and draws power from the motherboard, so not perfect - but at least it draws 5V not 3.3V, so won't affect the underdimensioned VRM adversely.

Thanks for the link. It is an interesting project. I didn't buy this board with the intention of it becoming a big project, so will have to park it for now. But certainly will consider doing this VRM upgrade later so I can use an MMX chip in it. It's always good to have backup options just in case the primary board fails.

I wonder how much making such a VRM board would cost (including all the components). Any idea?

dionb wrote on 2024-11-05, 14:32:

i430VX isn't a speed demon, but it's only a few percentage points behind the i430TX, which is Intel's fastest chipset for the MMX and clock-for-clock one of the fastest of the So7 chipsets overall. So choosing i430VX won't handicap it much. Not having L2 cache (like on this board...) will however handicap it significantly. Turning off L1 cache as well will get you seriously slow though.

If you wanted to choose the slowest chipsets for Pentium MMX, go for SiS 5511 with 6202 UMA graphics, or SiS5596 (same compontents integrated into the same chip). Not only does the integrated graphics eat half your memory bandwidth, you can also run on a single 32b SIMM, further halving the performance.

Yeah, my other board is 430 TX. I haven't been able to find any comparisons between the TX and VX in terms of performance. But I am aware that the VX is a budget chipset and not considered to be as good. It will be interesting to play with. Thanks for the info on the SIS chipsets. Looks like there's none for sale on ebay locally currently, but will look out for it.

RetroPCCupboard wrote on 2024-11-05, 15:44:

I haven't been able to find any comparisons between the TX and VX in terms of performance.

There's a feature set comparison between TX and VX in this Anandtech article.

No benchmarks, but it should still give you some useful info.

Joseph_Joestar wrote on 2024-11-05, 16:12:

There's a feature set comparison between TX and VX in this Anandtech article.

No benchmarks, but it should still give you some useful info.

Many thanks for the link.

Actually, I was mistaken, there are some SIS 551x socket 7 boards locally. However, they seem similar to the one that I just bought in that they don't seem to allow dual voltage CPUs and would need modification.

RetroPCCupboard wrote on 2024-11-05, 15:44:

[...]

Yeah, my other board is 430 TX. I haven't been able to find any comparisons between the TX and VX in terms of performance.

Here's a comparison I did a while back:
http://dionb.eu/chipset1.html

Compare the P-INT and P-FLOAT scores. Pretty much equal with EDO; TX is 7% or so faster in terms of memory performance (i.e. less difference in real-world applications). Also note that the difference between boards with same chipset can be bigger than the difference between chipsets.

But I am aware that the VX is a budget chipset and not considered to be as good.

It's not actually, it was Intel's flagship desktop chipset for about nine months, released in parallel to the i430HX, with the HX designed more for servers and workstations. The HX supported more RAM but the VX was faster paired with SDRAM. The only reason it looks mediocre in retrospect is that it was completely outclassed by its successor and by later competitors (ALi Aladdin IV in particular). Right now there's absolutely no reason to go for VX if you have access to TX, but end 1996, beginning 1997 it was the fastest option out there. There's a reason so many people bought one.

RetroPCCupboard wrote on 2024-11-05, 16:36:

[...]

Many thanks for the link.

Actually, I was mistaken, there are some SIS 551x socket 7 boards locally. However, they seem similar to the one that I just bought in that they don't seem to allow dual voltage CPUs and would need modification.

That's just par for the course in late 1996. Look for the 5596 for fully integrated stuff on a board with built-in VRM. They were later (end 1997, early 1998) and squarely positioned at the low end, so don't expect fancy boards. Then again, you now have a PC Chips board with warning about its linear 5V->3.3V VRM, so it's not likely to be any worse than that 😉

Yeah I've messed with some VX boards that were no better than FXes, and others that bested the mediocre TXs. Probably their "niche" at the moment is the lowest price ATX board, there weren't many, but everyone will be looking for TX or MVP3 or Ali. RAM can be a pain in the butt with them though, two 32MB is the low stress complement.

dionb wrote on 2024-11-05, 18:02:

Here's a comparison I did a while back:
http://dionb.eu/chipset1.html

Compare the P-INT and P-FLOAT scores. Pretty much equal with EDO; TX is 7% or so faster in terms of memory performance (i.e. less difference in real-world applications). Also note that the difference between boards with same chipset can be bigger than the difference between chipsets.

Hmm. That is interesting information. Must have taken you a while to compile that!

It's not actually, it was Intel's flagship desktop chipset for about nine months, released in parallel to the i430HX, with the HX designed more for servers and workstations. The HX supported more RAM but the VX was faster paired with SDRAM. The only reason it looks mediocre in retrospect is that it was completely outclassed by its successor and by later competitors (ALi Aladdin IV in particular).

OK. I saw an article on DOSDAYS website where the wording made me think what I did. But I am happy to be corrected.

Right now there's absolutely no reason to go for VX if you have access to TX, but end 1996, beginning 1997 it was the fastest option out there. There's a reason so many people bought one.

That's just par for the course in late 1996. Look for the 5596 for fully integrated stuff on a board with built-in VRM. They were later (end 1997, early 1998) and squarely positioned at the low end, so don't expect fancy boards. Then again, you now have a PC Chips board with warning about its linear 5V->3.3V VRM, so it's not likely to be any worse than that 😉

Socket 7 boards seem to have gone up in price since I last bought one (3 years ago maybe). Super-socket 7 though. Wow. Crazy pricing on those. Even several years ago.