I've just quickly checked photos of this board (unfortunately I have no such a board to check it in reality). And it seems there is no voltage regulator on this board, which could provide voltage regulation for CPU power supply.
So based on above I would say no support for CPU with power supply lower than 5V.

zami555 is absolutely right.
Some similar FIC 486 mainboards without onboard regulator have a special header to add a small proprietary VRM module, but the GIO-VT definitely hasn´t.

Thank you for the responses. I just checked the board as well and don't see VRM on it. See attachment.

Do you guys know if SX955 (DX/2 66) is a 5V or 3.3V CPU? I'm reading conflicting information. It is SL enhanced CPU so not sure if that implies it's 3.3V.

p6889k wrote on 2023-06-10, 09:48:

Thank you for the responses. I just checked the board as well and don't see VRM on it. See attachment.

Lack of a VRM doesn't always mean the board cant supply 3.3v, there are a number of boards that simply pass the 3.3v right from the PSU with some basic filtering, since the PSU is already doing the voltage regulation there isn't a huge need for the motherboard to also do it if its only handling 5v or 3.3v CPUs. The only time you would require a full fat VRM is if you are doing split plane voltages or require 3.45v/4v or some other voltage the PSU isn't already supplying.

I know of a few Intel boards that did this, IIRC there was a jumper on the board that you could set for 5v or 3.3v.

Trashbytes wrote on 2023-06-10, 15:33:

p6889k wrote on 2023-06-10, 09:48:

Thank you for the responses. I just checked the board as well and don't see VRM on it. See attachment.

Lack of a VRM doesn't always mean the board cant supply 3.3v, there are a number of boards that simply pass the 3.3v right from the PSU with some basic filtering, since the PSU is already doing the voltage regulation there isn't a huge need for the motherboard to also do it if its only handling 5v or 3.3v CPUs. The only time you would require a full fat VRM is if you are doing split plane voltages or require 3.45v/4v or some other voltage the PSU isn't already supplying.

I know of a few Intel boards that did this, IIRC there was a jumper on the board that you could set for 5v or 3.3v.

The FIC 486-GIO-VT is powered with an "AT-PSU" so there´s no 3.3V line. The Intel boards you mentioned are Socket 7 and have an ATX power connector.
On the FIC the 5V are distributed via one of the Vcc layers inside the PCB to reach all the Vcc pins of the CPU. I inspected this board (very) carefully a while ago to find some point where the CPU 5V power supply could possibly be interrupted. There is NONE.

You can of course use some Overdrive CPU or a socket 3 interposer with integrated VRM.