Tymo486DX2 wrote on 2024-09-17, 18:11:

I am looking for good motherboard for Intel 486 DX-2 66 MHz.

Lot of motherboards on the market. Is there any MB with AGP x2 port?

That combination does not exist...
https://en.wikipedia.org/wiki/Accelerated_Graphics_Port

The AGP slot first appeared on x86-compatible system boards based on Socket 7 Intel P5 Pentium and Slot 1 P6 Pentium II processors. Intel introduced AGP support with the i440LX Slot 1 chipset on August 26, 1997, and a flood of products followed from all the major system board vendors.[3]

Where it says Socket 7 I would say "Super Socket 7"
https://en.wikipedia.org/wiki/Super_Socket_7

486 didn't have AGP, Pentium Classic didn't have AGP, Pentium MMX boards with Intel chipsets didn't have AGP, Super Socket 7 and Slot 1 got AGP, in between the last two there were not quite super via chipsets that got it VP3 etc, but still 3 generations past 486es.

Then as far as PCI 486 boards go... they're early PCI implementations, not PCI 2.0 which is "getting warm" but not near enough AGP to make it simple.

Even super fast AMD DX5 systems barely take advantage of early 3D accelerators on PCI, so doing anything interesting or useful with an AGP accelerator with a DX2-66 is unlikely. But after you've proved us wrong, do SATA for 286.

BitWrangler wrote on 2024-09-17, 18:29:

But after you've proved us wrong, do SATA for 286.

I will aim even higher. SAS3 on 5150, anyone? 😜

So it's a pity, because I would like to buy it. And thank you for your answer.

Blah blah blah.
I have a 486 with AGP.

Okay, it is on a Matrox G400 behind a PCI-to-AGP bridge.

But you won't benefit from any AGP feature at all on a 486.

Gets me thinking... Agp to PCI bridge and get that onto a 486 board. With that you may even go to a pcie graphics card?

I'd love to see a DX2 with an ati X800

Go all the way, terascale or tesla or something and run an OS on the shaders so you can use the 486 as a DOS coprocessor.

Take a look at PCIe to PCI bridges. They are 3.3V only so you will need to mod the board (or slot, or bridge card) for work in 5V-only PCI on a 486 board, but other than that you can do some pretty insane stuff. Only limit for DOS VGA is that the card needs a VGA BIOS designed to work with BIOS, not UEFI.

As dionb mentioned, you'll run into the whole 5V PCI slot issue on the 486 platform, but check out this thread on AGP-to-PCI adapters - AGP to PCI adapters - any PCB designers here willing to make one?

Technically you can get 486 with 66MHz PCI.

The Serpent Rider wrote on 2024-09-17, 22:23:

Technically you can get 486 with 66MHz PCI.

I presume that would imply overclocking a 486DX-50, the motherboard's PCI bus and RAM to 66MHz (unless RAM can be run more slowly on some 486 chipsets ?) AND finding a PCI video card the will run on a 66MHz PCI bus (likely PCI 2.0 and 5V ).

Or is there another way to do this ?

Common way is a specific 486 motheboard (I think it was a Biostar but my memory is hazy) and using Cyrix or AMD 5x86 with 2x multiplier. Finding a video card that takes 66MHz PCI is probably a challenge.

Tiido wrote on 2024-09-17, 23:41:

Common way is a specific 486 motheboard (I think it was a Biostar but my memory is hazy) and using Cyrix or AMD 5x86 with 2x multiplier. Finding a video card that takes 66MHz PCI is probably a challenge.

Yes, I had forgotten about those, thank you.

Probably a SIS496 chipset, I'm guessing.

I wonder if a PCI 2.1, 66MHz capable video card would work on a PCI 2.0 bus overclocked to 66MHz.

Matrox Millennium II and Voodoo 3 are working.

The conclusion is that there could be a board for the 486 DX2 with an AGP x2 port manufacturer's version all on the board. Should we pray for it or give it up?
New boards for 486 a small batch for hobbyists, would there be a demand for it because I'm still in favor of it.😀😀😀

Watch this space and fork it for an AGP version I guess...
https://github.com/skiselev/sandy_river_486

Don't be under the impression it will be cheap though. $250 would be probably the middle of the range, plus or minus a lot.

If we overclock the FSB, including PCI, to 66 MHz, the clock of 486 DX2 will increase unnecessarily to this value. We need better interface clocks and modes for PCI and AGPx2 activited separately, including a fixed speed in the CPU socket of 33 MHz. If AGPx2 mode is active then 66 MHz. Dynamically switchable. Regular PCI-to-AGP bridge can only work as AGPx1 at 33 MHz only for 486 DX2.

BitWrangler wrote on 2024-09-18, 12:23:

Watch this space and fork it for an AGP version I guess...
https://github.com/skiselev/sandy_river_486

Don't be under the impression it will be cheap though. $250 would be probably the middle of the range, plus or minus a lot.

Something would be possible.
And what to prepare such a MB design, collect orders for such an MB into a list of willing and waiting people and order?

Socket PGA168 for 486 DX2 link
4x 72-pin EDO-RAM
1x AGPx2 at 66 MHz
2x PCI at 33 MHz
2x ISA
1x VESA VLB
cache memory 2 MB
integrated Multi I/O controller with 2xIDE
FSB 33/66 MHz dynamic

Chipset Intel 440 BX for pentium II and slot-1 was very nice.
Host Bus all at 66 MHz, PCI stable on 33 MHz, CPU 486 DX-2 could be too, AGPx2 as native Host Bus at 66 MHz. Quite simple and nice.