There were baby AT boards that were Slot 1 and Socket 370. I once had one that, with the use of a Lin Lin adapter, supported a 1.4 GHz Tualatin Celeron. AFAIK, Pentium 3 was the fastest ever supported in a baby AT motherboard.

This 440 BX Socket 370 Baby AT board is likely the best ever made in that form factor. https://www.anandtech.com/show/316

If you really wanted, you could probably go up to at least Pentium 4 if you use a backplane and SBC.. maybe even higher. But it wouldn't be much of a retro rig then.

As for upgrading at all, what is the current hardware?

Do you use it for DOS as well as Windows? this is mainly for knowing if it would be better to have at least one ISA slot for a soundcard.

What games and applications do you want to run that are not running fast enough on your current setup?

M812lmr was an AT style socket A motherboard

Should work with most any Duron

cyclone3d wrote on 2021-12-29, 18:05:

If you really wanted, you could probably go up to at least Pentium 4 if you use a backplane and SBC.. maybe even higher. But it […]
Show full quote

If you really wanted, you could probably go up to at least Pentium 4 if you use a backplane and SBC.. maybe even higher. But it wouldn't be much of a retro rig then.

As for upgrading at all, what is the current hardware?

Do you use it for DOS as well as Windows? this is mainly for knowing if it would be better to have at least one ISA slot for a soundcard.

What games and applications do you want to run that are not running fast enough on your current setup?

Well, the case is from an IBM PC XT. I haven't seen any backplane SBCs that look short enough to fit in one of those.

Motherboard: ASUS P5-99B

CPU: 500MHz AMD K6-2

Memory: 512MB

Video: Nvidia GeForce 6200 PCI.

Audio: Sound Blaster 16 with wavetable board.

Mouse: Logitech C7 bus mouse with 8-bit ISA card.

As for applications, I just want to play old DOS and Windows 9x games that haven't been ported to modern Windows.

Currently I suspect that the power supply is holding me back. (It's only a 200w AT model) I found that Athena makes 400w ones, but I question how reliable they may be.

Jetway 849BS is another Socket A/462 Baby AT board.
It supports 133 MHz FSB CPUs (Athlon XP) and has an AGP slot, so I'd prefer it over the M812LMR.

Today I learned that there were a couple of Socket A baby AT motherboards made! Someone like Phil should do a comparison of the last of the baby AT motherboards made to declare a winner for the fastest ever baby AT board. A good contender for the title: http://www.motherboard.cz/mb/jetway/849BS.htm

Edit: I also didn't know that there were baby AT boards that had no ISA slots!

Op, your motherboard has an ATX power supply connector; have you considered using one? Much easier to get a good quality power supply that way, and all you lose is the reset button (since it becomes your power on button).

Ok, for the power supply, since it is an XT case, I would swap out the innards with a good ATX power supply and use an ATX to AT adapter unless your AT style board has ATX connectors.. most of the newer ones do.

Slot-1/Socket 370 is probably going to be your best best. Just need to look for something with AGP and at least 1 ISA slot and then worry about the chipset after that.

gex85 wrote on 2021-12-29, 18:35:

Jetway 849BS is another Socket A/462 Baby AT board.
It supports 133 MHz FSB CPUs (Athlon XP) and has an AGP slot, so I'd prefer it over the M812LMR.

But it doesn't have an ISA slot.

Repo Man11 wrote on 2021-12-29, 18:40:

Op, your motherboard has an ATX power supply connector; have you considered using one? Much easier to get a good quality power supply that way, and all you lose is the reset button (since it becomes your power on button).

I have, but I think I need a -5v line for my ISA cards. I could use a Voltage Blaster, but I would need a 3rd slot for it.

Back in the early oughts, when my IBM Portable PC was worth about $40 if you found an enthusiast or $1.50 in scrap, I was contemplating stripping it out and installing an AT board. This was when they had still been produced in the living memory of a goldfish. The conclusion I came to at that time was that a 440BX board with a Tualatin was likely the best I could do. I have parts now I could maybe do it with, but I'm unlikely to find another IBM Portable at $40 or below.

Lylat1an wrote on 2021-12-29, 18:47:

Repo Man11 wrote on 2021-12-29, 18:40:

Op, your motherboard has an ATX power supply connector; have you considered using one? Much easier to get a good quality power supply that way, and all you lose is the reset button (since it becomes your power on button).

I have, but I think I need a -5v line for my ISA cards. I could use a Voltage Blaster, but I would need a 3rd slot for it.

There are very few cards that need -5v See here:
ISA Cards & Devices Requiring -5V

Even if you do have a card that needs -5v, you can always use an ATX to AT adapter that adds it:
https://www.ebay.com/itm/174646835381

There used to be a person on eBay that sold pre-made cables that added the -5v but they stopped a couple years ago now. The one linked above is a newer design but more expensive.

cyclone3d wrote on 2021-12-29, 20:06:

There are very few cards that need -5v See here: ISA Cards & Devices Requiring -5V […]
Show full quote

Lylat1an wrote on 2021-12-29, 18:47:

Repo Man11 wrote on 2021-12-29, 18:40:

Op, your motherboard has an ATX power supply connector; have you considered using one? Much easier to get a good quality power supply that way, and all you lose is the reset button (since it becomes your power on button).

I have, but I think I need a -5v line for my ISA cards. I could use a Voltage Blaster, but I would need a 3rd slot for it.

There are very few cards that need -5v See here:
ISA Cards & Devices Requiring -5V

Even if you do have a card that needs -5v, you can always use an ATX to AT adapter that adds it:
https://www.ebay.com/itm/174646835381

There used to be a person on eBay that sold pre-made cables that added the -5v but they stopped a couple years ago now. The one linked above is a newer design but more expensive.

I didn't see either of my cards on that list. But if they do need -5v, would they be damaged if I run them without it?

Lylat1an wrote on 2021-12-29, 20:57:

cyclone3d wrote on 2021-12-29, 20:06:

There are very few cards that need -5v See here: ISA Cards & Devices Requiring -5V […]
Show full quote

Lylat1an wrote on 2021-12-29, 18:47:

I have, but I think I need a -5v line for my ISA cards. I could use a Voltage Blaster, but I would need a 3rd slot for it.

There are very few cards that need -5v See here:
ISA Cards & Devices Requiring -5V

Even if you do have a card that needs -5v, you can always use an ATX to AT adapter that adds it:
https://www.ebay.com/itm/174646835381

There used to be a person on eBay that sold pre-made cables that added the -5v but they stopped a couple years ago now. The one linked above is a newer design but more expensive.

I didn't see either of my cards on that list. But if they do need -5v, would they be damaged if I run them without it?

Nope, they just won't work properly.

cyclone3d wrote on 2021-12-29, 18:44:

Ok, for the power supply, since it is an XT case, I would swap out the innards with a good ATX power supply and use an ATX to AT adapter unless your AT style board has ATX connectors.. most of the newer ones do.

In case of using an ATX power supply without an ATX to AT adapter, the OP would have to connect the original power switch of the IBM PC XT power supply with some wires to the motherboard power switch header to act as a soft power switch, otherwise OP can't turn on the ATX power supply to power the motherboard (at least if OP wants to avoid using another button / switch).

cyclone3d wrote on 2021-12-29, 20:06:

There are very few cards that need -5v See here: ISA Cards & Devices Requiring -5V […]
Show full quote

Lylat1an wrote on 2021-12-29, 18:47:

Repo Man11 wrote on 2021-12-29, 18:40:

Op, your motherboard has an ATX power supply connector; have you considered using one? Much easier to get a good quality power supply that way, and all you lose is the reset button (since it becomes your power on button).

I have, but I think I need a -5v line for my ISA cards. I could use a Voltage Blaster, but I would need a 3rd slot for it.

There are very few cards that need -5v See here:
ISA Cards & Devices Requiring -5V

Even if you do have a card that needs -5v, you can always use an ATX to AT adapter that adds it:
https://www.ebay.com/itm/174646835381

There used to be a person on eBay that sold pre-made cables that added the -5v but they stopped a couple years ago now. The one linked above is a newer design but more expensive.

I made a PCB for that.
Re: New solutions to the ATX -5V problem

the newest... SBC and backplane, there's backplanes in BabyAT format with keyboard connector, and SBCs go up to basically anything.

cyclone3d wrote on 2021-12-29, 18:05:

If you really wanted, you could probably go up to at least Pentium 4 if you use a backplane and SBC.. maybe even higher. But it […]
Show full quote

If you really wanted, you could probably go up to at least Pentium 4 if you use a backplane and SBC.. maybe even higher. But it wouldn't be much of a retro rig then.

As for upgrading at all, what is the current hardware?

Do you use it for DOS as well as Windows? this is mainly for knowing if it would be better to have at least one ISA slot for a soundcard.

What games and applications do you want to run that are not running fast enough on your current setup?

I like the backplane idea. Would be a very fun build. Some even had agp!

I think that somewhere there is such a thing as a pentium 4 AT motherboard but I can’t find it, (aside from the sbc/backplane option)

Sphere478 wrote on 2021-12-30, 00:50:

I think that somewhere there is such a thing as a pentium 4 AT motherboard but I can’t find it, (aside from the sbc/backplane option)

A scant few images of the Commate P4XB are out there.