I hope it's not possible. Because if it is, I'll have to add SBCs to my collection, which is already too large and expensive for the small house I live in and my budget 😀

An SBC will not upgrade a standard motherboard as you would have bus collisions and crash.

What you propose is interesting such as
could you modify an sbc to serve as a processor overdrive card ?
The engineering effort to modify one would likely be extensive and you would need a patch cable to the motherboards existing cpu socket to take over post.

So yeah close to impossible

You should be able to.. however, you would probably need to removed at least some of the socketed chips (CPU, BIOS, RAM and maybe the KBC). Not sure about other stuff.

Why not just get an ISA backplane?

And that 386 SBC you linked is incredibly expensive. That particular one has the CPU integrated into the ALi chip:

1Features
2Onboard ALi M6117C, Intel® 386SX-40 compatible CPU
3Onboard three RS-232 and one RS-232/422/485 serial port
4C&T 65545 CRT/LCD controller with 1MB display memory
5Supports DiskOnChip® (SSD) up to 1 GB
6PC/104 expansion connector
7Optional Ethernet

http://www.emacinc.com/products/pc_compatible_sbcs/SBC-357

In the end, if you did use the old motherboard, you would essentially be turning it into a passive backplane.

Edit: Here is the same SBC you linked but way cheaper:
https://www.ebay.com/itm/EMAC-SBC-357-4M-386C … 80/333394133557

I would probably go with a 386DX SBC though as the SX only has a 16-bit data path.

Pair that with a backplane with however many slots your case has and you are ready to rock.

For that matter, you could even use a 486 SBC though ISA only 486 seems silly to me.

I've never even spent $100 on a single SBC. Most of them I've gotten for $50 or less. Just have to keep your eye out for good deals.

Have done this quite a few times in the past, even ran a full PICMG P3-era board just plugged into the ISA bus of the 'host' system. So long as the host system isn't initialized, it should work. So no CPU and/or BIOS does the trick.

Note that power draw can be a (big) issue, so if the SBC doesn't have its own (aux) power connector, you could end up overheating the +5V/+12V lines on the host board.

Thanks a lot for the replies so far guys!!

cyclone3d, Yes turning the old mobo into a passive backplane is exactly what this experiment is about - that would be the goal. Regarding the specific SBC I linked, I agree it may not be the ideal candidate but I wanted to link something specific to help illustrate what I'm thinking of doing. After all I just thought of this project at 2am this morning 😀 I think the ideal SBC would be a 386dx with onboard VGA, IDE, PS2 keyboard, and COM port for mouse - this way we only rely on the motherboard to access "secondary" devices like MFM controller card, sound card, etc. Why not just use a (real) ISA backplane? Well I have considered it but somehow I don't feel I could bring myself to "gut" a perfectly working IBM 5170 by replacing its mobo with a backplane. I know you could argue that I'd be doing essentially the same thing by using the original motherboard in the way I'm proposing but it feels different - if only emotionally. Leaving the original board in-place would also make it easier, in theory, to switch back. In the perfect world there would be a single toggle switch for this purpose on the back of the case but I know that level of refinement would be much more difficult to achieve.

dionb, That's what I was looking for - someone who can say they've done this before - that means there's at least a chance of me getting it working! I think I'm going to have to try it out.

debs3759, I know, right! This project may be objectively silly but it's just somehow appealing isn't it! I'm in the same boat as far as the small house but one computer that can be both a 286 and a 386 takes up less space than one of each 😀

AngieAndretti wrote on 2020-11-11, 00:29:

debs3759, I know, right! This project may be objectively silly but it's just somehow appealing isn't it! I'm in the same boat as far as the small house but one computer that can be both a 286 and a 386 takes up less space than one of each 😀

Imagine what it's like having 30+ cases, over 100 motherboards (probably nearer 140), over 500 graphics cards, probably 2000 or 2500 CPUs, and crates of other parts with only a sitting room and bedroom.... I really need to finish cataloguing my collection 😀 I don't do things by halves 😀 Only thing I don't have lots of is sound cards, as I'm deaf in one ear and tone deaf in the other.

It would be interesting to set up a few ISA and PCI SBCs on appropriate backplanes though, I'm sure when I get organised that I can find space for a custom case for them. Not sure I'd want to waste a perfectly good motherboard to do it though.

debs3759 wrote on 2020-11-11, 00:41:

AngieAndretti wrote on 2020-11-11, 00:29:

debs3759, I know, right! This project may be objectively silly but it's just somehow appealing isn't it! I'm in the same boat as far as the small house but one computer that can be both a 286 and a 386 takes up less space than one of each 😀

Imagine what it's like having 30+ cases, over 100 motherboards (probably nearer 140), over 500 graphics cards, probably 2000 or 2500 CPUs, and crates of other parts with only a sitting room and bedroom.... I really need to finish cataloguing my collection 😀 I don't do things by halves 😀 Only thing I don't have lots of is sound cards, as I'm deaf in one ear and tone deaf in the other.

It would be interesting to set up a few ISA and PCI SBCs on appropriate backplanes though, I'm sure when I get organised that I can find space for a custom case for them. Not sure I'd want to waste a perfectly good motherboard to do it though.

Wow! That's about the same as me... except I don't have as many CPUs but I have a massive number of sound cards.

AngieAndretti wrote on 2020-11-11, 00:29:

debs3759, I know, right! This project may be objectively silly but it's just somehow appealing isn't it! I'm in the same boat as far as the small house but one computer that can be both a 286 and a 386 takes up less space than one of each 😀

I too was bewitched by the world of SBCs and I think the same way: a computer that has as many systems as possible inside it to have the widest possible retrogaming experience in the smallest possible space.

I have acquired a lot of knowledge over time on the subject and I can tell you that the absolutely perfect machine, the DEFINITIVE machine for what you are looking for is the Amiga4000.

The amiga4000 was designed to be a backplaine itself. Let me explain: this machine has inside a riser card with the proprietary expansion slots of the amiga world called ZORRO and alongside it has 3 16bit ISA slots that communicate with each other but are connected to the motherboard of the amiga4000 only in the pins which bring power to the isa bus. It is a perfect machine, because in a really compact case you have all the software of the wonderful and revolutionary Commodore machine until the early 90s, where it will actually be overtaken by the PC, PC that you have in the 3 isa slots inside the machine. For example I have a sbc with pentium1 up to K6III, with vga, ps / 2 and ethernet connector, another slot has a sound blaster 16 and the third is free for another sound card or any other ISA card. In reality, for the amiga 4000 there is an even more intriguing thing which is called bridgeboard which mounts a 386sx pc (in its maximum expression) and which communicates with the amiga system. The topic is so broad that I won't dwell on it, but if you want I can explain it to you if you ask me some specific questions. Believe me, if you like the idea of ​​having more systems in one machine, in the 4000 you will have the creme de la creme from the mid 80s to the second half of the 90s, the golden years in one machine only.

I've searched eBay for an Amiga 4000 from time to time, but they seem to have become very rare and extremely expensive... and that's coming from someone who just dropped $450 on a 35-year-old IBM PC 😀 ... but yes, I'd love to have one some day!