Are you using an LCD monitor. Run scitech 6.53 or 6.7, it will load a VBE3 bios and enable refresh rate changes in dos. Then run UNICENTR.EXE and it will let you set the refresh rate using + and - keys so the monitor will not blank screen in the resolutions you want.

Riikcakirds wrote on 2026-09-29, 19:47:

Are you using an LCD monitor. Run scitech 6.53 or 6.7, it will load a VBE3 bios and enable refresh rate changes in dos. Then run UNICENTR.EXE and it will let you set the refresh rate using + and - keys so the monitor will not blank screen in the resolutions you want.

Thx a lot!
I have tried your solution: same result.

Today I found another solution, but it is more than weird:

Weeks ago, I bought a P233MMX for my Gigabyte GA-586HX v1.54. I thought it’d be cool since the Gigabyte has auto-voltage and only 4 DIP switches.

Today, I tried it out, but the Gigabyte didn't recognize it, showing only a P166MMX. I was angry and disappointed, and thought someone had cheated me by relabeling a P166MMX as a P233MMX.

Then, I plugged the CPU into my ECS P5HX-A and set the multiplier to 3x via jumpers, which is its maximum.

Suddenly, the CPU ran as a P200MMX, showing me that the Gigabyte, not the CPU, has some issues.

I started Quake 1 to test stability, and suddenly I got the idea to check once again whether 640x480 works or still doesn't.

Guess what: with the new CPU, I now have not only 640x480, but also 800x600.

This means that the old ceramic P166MMX has some kind of bug, error, or damage.

Result:

Very happy that I can finally play Quake 1 in software mode at 800x600 on my ECS board.

Unhappy because the Gigabyte seems to have problems with its DIP switches; I will run further tests on why the 3.0x multiplier isn't working either.

I will test the ceramic P166MMX in all my Socket 7 boards to check whether Quake 1 refuses 640x480 on all of them => this would make me sell this CPU ASAP.

I am really astonished by what weird and odd behavior I so often discover on old hardware.

It is like a rollercoaster experience, but hey, somehow it is cool!

EDIT: @Riikcakirds => Now I have put the ceramic P166MMX into the Gigabyte board. I started Quake 1. Up to 360x480, everything is fine. But 640x480 immediately delivers a blank screen. No chance. This is proof that the ceramic P166MMX is the root of the problem. I have no idea how a CPU can cause a display resolution limitation?

Once again, a comparison of the current setups:

PC: ECS P5HX-A (Intel 430HX), P233MMX, 64MB EDO, Spea Mirage V7 Trio64 2MB, 32GB SanDisk SD card => Quake 1 runs up to 800x600 in software mode.

PC: Gigabyte GA-586HX v1.54, P166MMX, 64MB EDO, the same Spea Mirage, same SanDisk card => Quake 1 only runs up to 360x480.

PC: Same as number 2, but with a P150 instead of the P166MMX => Quake 1 allows resolutions up to 800x600.

DOS Quake requires 16MB+ of system memory and VESA 2.0 to access the higher modes.

leileilol wrote on Yesterday, 00:25:

DOS Quake requires 16MB+ of system memory and VESA 2.0 to access the higher modes.

Both systems have > 16MB EDO RAM and VESA 2.0 via S3 driver and an identical (!) Spea Mirage V7 Trio64 2MB PCI graphic card.

But only the system with the ceramic P166MMX limits to 360x480: there is no rational explanation

I can make a video of both to show you, but it is easier to sell the P166MMX.

Once again: Q1 1.08 offers me up to 800x600 on:

P150, P233MMX, but not on P166MMX ceramic with the same graphic card

I think there must be some weird exception error based on the combination of P166MMX ceramic, the both i430HX boards and Q1 v1.08.

Besides, I remember the following peculiar exception, sorry for prolonging my answer here:

2 months ago I substituted the Spea with a Tseng ET6000 4MB only to test performance (all fast, expensive and scarce graphics cards are in a shelf, not in gaming PCs)

On the Tseng ET6000 Q1 allowed up to 1024x768, I was astonished and thought, ok, the S3 has some kind of limits or I need Sci Tech Doctor etc.

=> ECS P5HX-A, P166MMX, 64MB, Tseng ET6000 4MB, MSDOS 6.22, Quake1 v.1.08

But after so many tests I can definitely say, that the P166MMX ceramic has some kind of a bug or an internal error.

Did you read leileilol's signature that says FUCK AI? I did. You should heed that advice. As soon as I read "this is the answer from Gemini" I was done with your post.

Maraakate wrote on Yesterday, 12:34:

Did you read leileilol's signature that says FUCK AI? I did. You should heed that advice. As soon as I read "this is the answer from Gemini" I was done with your post.

you re right, I have edited my post.
In case someone is seeking a cheap P166MMX CPU, I will sell mine for about 15€.

Do you have a photo of the P166MMX? Not that I’m interested in buying it but I’m wondering about the specific details. Perhaps I have the same CPU and I can test it whenever I dig out my Socket 7 stuff 😉.