You would more than likely end up with the following:

1. BIOS conflict between the motherboard BIOS and the SBC BIOS.
2. Damaging the motherboard due to power overdraw.
3. Damage to the SBC doing the same thing.

They are designed to be used only with PICMG ISA/VLB/PCI backplanes.

Dmetsys wrote on 2020-11-29, 06:16:

You would more than likely end up with the following: […]
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You would more than likely end up with the following:

1. BIOS conflict between the motherboard BIOS and the SBC BIOS.
2. Damaging the motherboard due to power overdraw.
3. Damage to the SBC doing the same thing.

They are designed to be used only with PICMG ISA/VLB/PCI backplanes.

I would love to see a VLB backplane.

PICMG 1.0 is ISA + PCI
PICMG 1.3 is PCIe and may or may not have PCI

PIAGP is AGP + PCI + ISA

Anyway, even if you did use a 486 SBC on a ATX board, you would only end up with ISA slots anyway. Nothing else would work.

And you would have to wire up power differently anyway.

Might as well just get an ISA backplane and mount it in an ATX case if that is what you really want.

If you wanted to go fancy, you could use a PICMG 1.0 backplane and a PICMG 1.0 486 SBC but be aware that the PCI slot addresses are kind of important and you need a backplane that supports the addresses that your SBC supports. Any slots that the addresses don't match on will not work.

There are very few PICMG 1.0 486 SBCs and they tend to be expensive when they do pop up for sale.

Ahh yes, it's not VLB. It's the power connector for other types of SBC's. Learn something new everyday I suppose.

cyclone3d wrote:

There are very few PICMG 1.0 486 SBCs and they tend to be expensive when they do pop up for sale.

And LGR didn't help when he made a video about them.

cyclone3d wrote on 2020-11-29, 06:40:

There are very few PICMG 1.0 486 SBCs and they tend to be expensive when they do pop up for sale.

Still cheaper than a lot of 486 desktops that you see with similar specs, while lacking hard drives. I was almost tempted to go that route, despite being limited to an ISA BUS.

Not really. The issue is the CASE.

These systems were often designed around having 20-slot boards. like this glorious bastard: https://www.ebay.com/itm/392296512414

That board used by LGR: https://www.ebay.com/itm/114451789060

They are not cheaper. They are not better. (generally speaking) They are cool and fun, but just aren't designed to play games. They were designed to be a hard working mule of a system.

luckybob wrote on 2020-11-29, 07:19:

Not really. The issue is the CASE.

That's the point I'm trying to convey. There is no logic in charging 50% of the cost of the system because of the enclosure, especially if you plan on swapping components on a routine basis. Shipping is also a cost factor, which I know doesn't apply to those that are lucky to live in metro areas where hardware can be plentiful. DOOM doesn't make the 99th percentile of the gaming for that era. It just happens to be the well known benchmark, where you need an ET4000, CL542x, or WD90C33 to make it playable.

Dmetsys wrote on 2020-11-29, 06:44:

Ahh yes, it's not VLB. It's the power connector for other types of SBC's. Learn something new everyday I suppose.

Power and data lines for PCI connections you should have said. "Near" ISA part of these SBCs connector has the ISA component for the backplane, and the "far" PCI VL-like part has the PCI component. PIAGP SBCs have the ISA part of the component replaced with something which resembles one of those EISA brown connectors with more pins but a bit smaller, so is incompatible with PCIMG SBC cards, and may haven't ISA compatibility at all (it doesn't connect the ISA part of the backplane).

IS BETTER to have this completely clear before buying and testing these thing. LGR made a terrible mistake connecting his SBC arbitrary to any ISA slot in the backplane. It should go in the slot marked for the SBC in the backplane, or you would have bus reflection problems, depending how the SBC bus termination was wired.

I see LGR has once again, brought something out of the woodworks. *rest in peace SBC 486 prices*.

So is there any performance hit with a SBC having it connected over a ISA-like slot? Instead of using a normal 486 motherboard-cpu combo?

It was to my understanding SBCs where for industrial use and not geared towards high performance/gaming.

Yeah, with PIAGP, you need the backplane as well as the PCI-ISA bridge module. There are a couple difference PIAGP SBCs that don't even support DMA on the ISA bus.

As for an ISA 486 SBC, there would be no performance hit compared to a regular 486 motherboard.

It isn't due that they are not build specifically for high performanc but then again, they are built very well and there really should not be a performance difference between an SBC and a regular motherboard that uses the same chipset.

hyoenmadan wrote on 2020-11-29, 15:43:

Dmetsys wrote on 2020-11-29, 06:44:

Ahh yes, it's not VLB. It's the power connector for other types of SBC's. Learn something new everyday I suppose.

Power and data lines for PCI connections you should have said. "Near" ISA part of these SBCs connector has the ISA component for the backplane, and the "far" PCI VL-like part has the PCI component. PIAGP SBCs have the ISA part of the component replaced with something which resembles one of those EISA brown connectors with more pins but a bit smaller, so is incompatible with PCIMG SBC cards, and may haven't ISA compatibility at all (it doesn't connect the ISA part of the backplane).

IS BETTER to have this completely clear before buying and testing these thing. LGR made a terrible mistake connecting his SBC arbitrary to any ISA slot in the backplane. It should go in the slot marked for the SBC in the backplane, or you would have bus reflection problems, depending how the SBC bus termination was wired.

That's being pedantic, just so you know. Near and far are not technical terms when describing connectors. When looking at the backplane, there is no marker indicating where to plug in the SBC. It's a 'dumb PCB' with no controller to speak of, so it doesn't matter where you plug it in.

Dmetsys wrote on 2020-11-29, 17:22:

It's a 'dumb PCB' with no controller to speak of, so it doesn't matter where you plug it in.

I don't think my post is pedantic at all, but if it makes you feel better, then call it CNN1 and CNN2, or J1 and J2, or whatever you want to call them. I just used a terms was common when I worked years ago with these things... Is easier to me reference them like that, and btw I marked the words with quotes to highlight these may not be the correct terms.

And you have to check your SBC and Backplane to determine if the SBC has termination resistors networks for the exposed buses, or them are in the backplane. The backplane used in LGR videos has capacitors and resistos near the "VLBus" like slots clearly marked for backplane usage, which instead he used to connect his sound card. Depending in the combo, it may have bad influence in the rest of the components.

You always have to check your SBC and Backplane combo to watch for these small details. But as rule of gold, if you have one of these PCI/ISA combo backplanes, you have to put the card in the first or the second "VLBus" like slot. That's how it was designed to work. If you have one of these ISA only backplanes, as in LGR last part of his video, and it doesn't have the SBC slot marked, then you may use the last slot, EXCEPT when the SBC has weak ISA signals and can't drive all the slots in the backplane... In such case, you may install the isa adapter in one of the middle slots, and only use only the remaining slots over or under it, depending how the backplane and the SBC are terminated.

(This remembers you guys something? Yes, is just like what happens in SCSI hell.)

If you want a platform good for upgrading and squeezing every last drop of performance from a system, then SBCs are probably not the best choice. On SBCs with only an ISA edge connector, your only upgrade options are ISA cards. You're stuck with whatever onboard graphics, I/O, networking, etc, are connected internally to the VLB/PCI bus. I'm sure it's possible to get your graphic accelerator cards working with the right SBC and backplane combination, but I don't think it would be any more practical than building with a regular motherboard. Personally, I use ISA SBCs to save space. I custom built a small case with a 4 slot ISA backplane, sound card, removable media, power supply, etc and I swap out SBC's depending on what kind of computer I want to play with. Impulse buying an SBC takes up way less space than impulse buying a motherboard, case, PSU, etc.

Those prices are so crazy. I used to be really interested in putting together a huge parallel computer 2 decades ago. These were nearly being thrown away. eBay auctions were often starting at $0.01 for these and ending at a few dollars. Sadly, I never got any of these and went with a 4 socket Pentium Pro machine that I've sadly since parted with instead.

hyoenmadan wrote on 2020-11-29, 18:44:

I don't think my post is pedantic at all, but if it makes you feel better, then call it CNN1 and CNN2, or J1 and J2, or whatever […]
Show full quote

Dmetsys wrote on 2020-11-29, 17:22:

It's a 'dumb PCB' with no controller to speak of, so it doesn't matter where you plug it in.

I don't think my post is pedantic at all, but if it makes you feel better, then call it CNN1 and CNN2, or J1 and J2, or whatever you want to call them. I just used a terms was common when I worked years ago with these things... Is easier to me reference them like that, and btw I marked the words with quotes to highlight these may not be the correct terms.

And you have to check your SBC and Backplane to determine if the SBC has termination resistors networks for the exposed buses, or them are in the backplane. The backplane used in LGR videos has capacitors and resistos near the "VLBus" like slots clearly marked for backplane usage, which instead he used to connect his sound card. Depending in the combo, it may have bad influence in the rest of the components.

You always have to check your SBC and Backplane combo to watch for these small details. But as rule of gold, if you have one of these PCI/ISA combo backplanes, you have to put the card in the first or the second "VLBus" like slot. That's how it was designed to work. If you have one of these ISA only backplanes, as in LGR last part of his video, and it doesn't have the SBC slot marked, then you may use the last slot, EXCEPT when the SBC has weak ISA signals and can't drive all the slots in the backplane... In such case, you may install the isa adapter in one of the middle slots, and only use only the remaining slots over or under it, depending how the backplane and the SBC are terminated.

(This remembers you guys something? Yes, is just like what happens in SCSI hell.)

This is some good info. I didn't work with them back in the day as far as building them so this should help.

ZombieMatrix wrote on 2020-11-29, 19:35:

Those prices are so crazy. I used to be really interested in putting together a huge parallel computer 2 decades ago. These were nearly being thrown away. eBay auctions were often starting at $0.01 for these and ending at a few dollars. Sadly, I never got any of these and went with a 4 socket Pentium Pro machine that I've sadly since parted with instead.

Yeah, the prices on SBC setups are usually kinda crazy now, but a decently priced SBC comes up every now and then. I haven't spent over I think $85 for any of mine, with the ones I have bought normally half that or less.

The prices on PICMG 1.3 backplanes are what is annoying but I finally scored one for cheap not that long ago.

The PIAGP backplanes with the PCI-ISA bridge modules generally go for around $100 + shipping but that is kinda expected seeing as how they are not that common.... I have one system built and have parts to build 2 more.

Dmetsys wrote on 2020-11-29, 17:22:

That's being pedantic, just so you know. Near and far are not technical terms when describing connectors. When looking at the backplane, there is no marker indicating where to plug in the SBC. It's a 'dumb PCB' with no controller to speak of, so it doesn't matter where you plug it in.

[Bill Lumbergh voice]
YEEEAA... I'm going to stop you there...
[/Bill Lumbergh voice]

It actually does matter, and it matters more on the bigger boards. It is an identical concept as SCSI termination. Is it POSSIBLE that you don't need to terminate properly? Yes. Is it good practice? NO.

The larger boards, such as the massive 21-slot boards have markers and sockets for bus termination resistors. You are supposed to put the SBC on one end, and terminate the other. Yea, it might not be silkscreen on the motherboard for the luddites, but if you find a proper manual, i'd bet my left nut it tells you to only put the SBC in certain slots. (it depends on the SBC, addon cards, phase of the moon, etc)

When you see multiple "long" pci/isa slots. The baseboard is giving you a choose of those slots. It is actually very common for SBC boards to be 2-slots thick. There are a select few boards that even allow multiple SBC's in one chassis, but i've never seen one in person.

and if you come back and show me a board, and it clearly has the SBC slots in the middle, take a closer look. the ISA bus stops mid-way, then continues as pci. The SBC is still on the end of each bus. PCI is a bit different, but let's not get too deep into the weeds here.

Nitroraptor53 wrote on 2020-11-29, 05:24:

What would happen if I plugged a 486 SBC into a Socket 7 or Slot 2 motherboard? The RAM, CPU, BIOS and Controller would all be on the SBC. Could I use this to make an ATX or uATX 486?

in my opinion you could follow a path that i have been thinking about for some time, since I am also passionate about SBC ...

Can anyone correct me if I am wrong as I have not yet tried to do what I am about to describe.

You could get a normal Socket7 / Slot1 computer like you said, but a desktop type, with ISA / PCI expansion slots on a riserboard. This type of computer is very common, especially among OEMs. At this point take the riserboard and identify the pins that power the ISA bus (maybe even the PCI one but someone should confirm my idea) and mark them, the other pins that remain are those of the data bus. At this point, cut all the pins of the data bus so that the riserboard has the connection with the mainboard only through the power pins. And at this point your riserboard is effectively a backplane. In theory you could cut the bus pins even AFTER the first ISA slot so as to leave it connected to the host computer and be able to insert a sound card for example. You can still find spare riserboards on ebay, so as to have your computer working with two riserboars (not simultaneously): one original and one modified.

I don't know if I was able to explain myself.

AlessandroB wrote on 2020-11-30, 22:06:

in my opinion you could follow a path that i have been thinking about for some time, since I am also passionate about SBC ... […]
Show full quote

Nitroraptor53 wrote on 2020-11-29, 05:24:

What would happen if I plugged a 486 SBC into a Socket 7 or Slot 2 motherboard? The RAM, CPU, BIOS and Controller would all be on the SBC. Could I use this to make an ATX or uATX 486?

in my opinion you could follow a path that i have been thinking about for some time, since I am also passionate about SBC ...

Can anyone correct me if I am wrong as I have not yet tried to do what I am about to describe.

You could get a normal Socket7 / Slot1 computer like you said, but a desktop type, with ISA / PCI expansion slots on a riserboard. This type of computer is very common, especially among OEMs. At this point take the riserboard and identify the pins that power the ISA bus (maybe even the PCI one but someone should confirm my idea) and mark them, the other pins that remain are those of the data bus. At this point, cut all the pins of the data bus so that the riserboard has the connection with the mainboard only through the power pins. And at this point your riserboard is effectively a backplane. In theory you could cut the bus pins even AFTER the first ISA slot so as to leave it connected to the host computer and be able to insert a sound card for example. You can still find spare riserboards on ebay, so as to have your computer working with two riserboars (not simultaneously): one original and one modified.

I don't know if I was able to explain myself.

Someone will surely correct me if I'm wrong, but I don't think you can just cut the traces on a riser card to make a second backplane without any problems. You probably have to consider the electrical characteristics of your modified riser card to make sure both ISA buses function properly. A simpler solution would be to find a small backplane that fits in the case and use adapters to connect the power supply to it.