The Intel dx4 can be jumpered for 2x or 3x, only one jumper pin on 486 systems

If you get the Overdrive version it has no jumper at all.

Some motherboards have issues with the Intel dx4 and L1 internal cache, other very old boards improperly detect the dx4 with the wrong speed and crash (need a bios update)

If you bought a non-retail Intel DX4 voltage is the other concern but it won’t affect the clock

fsinan wrote on 2024-03-12, 09:28:

Hi there, […]
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Hi there,

I've tested and successfully worked every cpu on this board within 486 range from DX-33 to Cyrix 5x86 but Intel DX4-S does not boot at 100Mhz but at 66Mhz. AMD DX4 works at 100Mhz, 120Mhz, X5 works ar 133 without problems.

Tried every board model settings at the theretroweb with same hw and jumper layout. Jumper setting for multiplier for Intel processors does not work properly and cpu boots as DX4-S at 66Mhz. Checked cpuid, it is geniuine.

Is there a multiplier trick for Intel DX4 processors that I should know?

Thanx.

Did you verify the speed with speedsys or something, or do you rely only on the output of the Bios?
The 2x multiplier jumper for a DX4-100 is the exact same jumper setting that does the 4 times muliplier on the Am5x86-133.

tested and controlled with different benchmarks and programs.

Does the board have an Intel/AMD jumper?

AMD DX2/DX4 (non WB) have a different CLKMUL pin than Intel and others. http://www.pchardwarelinks.com/486pin2.htm

fsinan wrote on 2024-03-15, 14:32:

tested and controlled with different benchmarks and programs.

You give only very little information, but I try once more.
You wrote an AMD 4x86DX4 works at 100MHz.
What is the exact model of the AMD? I mean what is printed on it.

MikeSG wrote on 2024-03-15, 18:17:

Does the board have an Intel/AMD jumper?

AMD DX2/DX4 (non WB) have a different CLKMUL pin than Intel and others. http://www.pchardwarelinks.com/486pin2.htm

You can select the cpu type with two jumpers. I selected it, it is ok.

CoffeeOne wrote on 2024-03-16, 19:49:

You give only very little information, but I try once more. You wrote an AMD 4x86DX4 works at 100MHz. What is the exact model of […]
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fsinan wrote on 2024-03-15, 14:32:

tested and controlled with different benchmarks and programs.

You give only very little information, but I try once more.
You wrote an AMD 4x86DX4 works at 100MHz.
What is the exact model of the AMD? I mean what is printed on it.

A486DX4-100SV8B and A80486DX4-120SV8B and X5-133 cpus works at their intended frequencies. And all other cpus from U5S-40 to Cyrix 5x86-100GP in my inventory.

fsinan wrote on 2024-03-17, 09:22:

CoffeeOne wrote on 2024-03-16, 19:49:

You give only very little information, but I try once more. You wrote an AMD 4x86DX4 works at 100MHz. What is the exact model of […]
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fsinan wrote on 2024-03-15, 14:32:

tested and controlled with different benchmarks and programs.

You give only very little information, but I try once more.
You wrote an AMD 4x86DX4 works at 100MHz.
What is the exact model of the AMD? I mean what is printed on it.

A486DX4-100SV8B and A80486DX4-120SV8B and X5-133 cpus works at their intended frequencies. And all other cpus from U5S-40 to Cyrix 5x86-100GP in my inventory.

Did you use the exact same jumper setting for the A486DX4-100SV8B as for the Intel DX4-S?

EDIT: setting the multiplier of a DX4-100 to 2 is a pure hardware setting as far as I know.
The only way to do it, is to set JP21 to 1-2 on this board, if I read the "partial documention" of retroweb correctly.
So when this is not set and the DX4-100 is running at 66MHz (not only reported by Bios, but really!) , then it is 100% a mystery.

If yes, please make a picture of your Intel DX4-100 from both sides up and backside.

More EDIT: I am asking for that, because it only can be a fake CPU in that case.

EVEN MORE EDIT:
Before taking a picture from the (fake) intel DX4.
Run either speedsys or cachechk. Both programs are able to show the amount of L1 cache. An Intel DX2-66 has 8kB of L1 cache, where an Intel DX4-100 has 16kB of L1 cache.
Please add a picture of the output of those 2 programs to your answer.
When L1 cache shows up with 8kB, then of course add pictures of the CPU itsself as requested by me above. I never saw a fake Intel DX4-100. Would be a good fit if the board has fake cache though.

Jp21 set to 1-2 it boots as dx4-S at 66Mhz. 2-3 setting boots at 66Mhz no change.

Cpuid reports are dx4 at 66mhz with 3x multplier.

Speedsys reports as 486dx4-66mhz. 16Lb cache.

When jp21 set to 2-3 then it does not boot as 100Mhz, black screen.

Additional note;
When jp-22 which is not listed on board is set to 1-2, or 2-3 does not differ it boots at 100Mhz. Pictures limited couldnt add speedsys reports 35.43. Lower than Amd dx4-100wb.

Later note: optimized settings at bios speedsys reports 42.58.

fsinan wrote on 2024-03-17, 16:31:

Jp21 set to 1-2 it boots as dx4-S at 66Mhz. 2-3 setting boots at 66Mhz no change. […]
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Jp21 set to 1-2 it boots as dx4-S at 66Mhz. 2-3 setting boots at 66Mhz no change.

Cpuid reports are dx4 at 66mhz with 3x multplier.

Speedsys reports as 486dx4-66mhz. 16Lb cache.

When jp21 set to 2-3 then it does not boot as 100Mhz, black screen.

Additional note;
When jp-22 which is not listed on board is set to 1-2, or 2-3 does not differ it boots at 100Mhz. Pictures limited couldnt add speedsys reports 35.43. Lower than Amd dx4-100wb.

Later note: optimized settings at bios speedsys reports 42.58.

Thx for the pictures.
So the CPU is fine. 16kB L1 as it should be!

What do you mean with JP21 2-3?
That is not listed here:
https://theretroweb.com/motherboard/manual/st … 2e566497050.pdf

JP21 should be always Open. Or for Am5x86 @133 or 160 set to 1-2.
Similar for Intel DX4 multiplier 2 JP21 should be set to 1-2.

Do you have other jumper settings? Maybe the description is not the right one.

But from your comment, you solved the problem already? So you found the right jumper setting to run it at 100MHz?
Everything is good?

fsinan wrote on 2024-03-17, 16:31:

Jp21 set to 1-2 it boots as dx4-S at 66Mhz. 2-3 setting boots at 66Mhz no change. […]
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Jp21 set to 1-2 it boots as dx4-S at 66Mhz. 2-3 setting boots at 66Mhz no change.

Cpuid reports are dx4 at 66mhz with 3x multplier.

Speedsys reports as 486dx4-66mhz. 16Lb cache.

When jp21 set to 2-3 then it does not boot as 100Mhz, black screen.
......

And sorry, but with that kind of infos it's hard to give advices:
You wrote:
JP21 set to 1-2, it boots as DX4 at 66 => Yes, that corresponds to the manual.
Then you wrote 2-3 setting boots at 66MHz. => 2-3 setting is not documented in the manual. I have no idea.
3 lines later:
When jp21 set to 2-3 then it does not boot as 100Mhz, black screen. => So what? 66 or black screen?

According to the manual it should be OPEN, so neither 1-2 nor 2-3.

But when the issue is solved, please ignore this post.

CoffeeOne wrote on 2024-03-17, 20:03:

What do you mean with JP21 2-3?

JP21 should be always Open. Or for Am5x86 @133 or 160 set to 1-2.
Similar for Intel DX4 multiplier 2 JP21 should be set to 1-2.

This! The CLKMUL pin on the 486DX4-like processors was intended to support 3 different states: Open, pulled up or pulled down, selecting 3x, 2.5x or 2x clock. Many boards support both pull-up and pull-down configurations, but most DX4-like processors do not support 2.5x clock, and do not start in that configuration. JP21 2-3 is likely selecting this configuration (which would result in 83MHz if the CPU supported it), and thus is expected to not work. JP21 completely removed from the board (neither 1-2 nor 2-3) is the correct setting for a DX4.

CoffeeOne wrote on 2024-03-17, 20:03:

What do you mean with JP21 2-3? That is not listed here: https://theretroweb.com/motherboard/manual/st … 2e566497050.pdf […]
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What do you mean with JP21 2-3?
That is not listed here:
https://theretroweb.com/motherboard/manual/st … 2e566497050.pdf

JP21 should be always Open. Or for Am5x86 @133 or 160 set to 1-2.
Similar for Intel DX4 multiplier 2 JP21 should be set to 1-2.

It didnt work with these settings, so there are same harware layout boards with other brands at theretroweb and I decided to try their settings. So set the JP21 according to them.

For example in this pdf that you sent the link, which is a terrible one, there is no JP22 setting. Handwritten on mobo picture page. Set according to that.

Anyway, it was working ok but this morning it didnt boot again, boots 1/10 of the tries. Dont know why but the settings do not work.

mkarcher wrote on 2024-03-17, 20:17:

CoffeeOne wrote on 2024-03-17, 20:03:

What do you mean with JP21 2-3?

JP21 should be always Open. Or for Am5x86 @133 or 160 set to 1-2.
Similar for Intel DX4 multiplier 2 JP21 should be set to 1-2.

This! The CLKMUL pin on the 486DX4-like processors was intended to support 3 different states: Open, pulled up or pulled down, selecting 3x, 2.5x or 2x clock. Many boards support both pull-up and pull-down configurations, but most DX4-like processors do not support 2.5x clock, and do not start in that configuration. JP21 2-3 is likely selecting this configuration (which would result in 83MHz if the CPU supported it), and thus is expected to not work. JP21 completely removed from the board (neither 1-2 nor 2-3) is the correct setting for a DX4.

Removed? Non-functional? Some boards with similar hw layout has settings for JP-21. Thats why I tried whenn the original settings didnt work and still not working.

It just randomly boots, just shows blank screen other times. 1/10 maybe. Settings are correct.

fsinan wrote on 2024-03-18, 06:33:

Removed? Non-functional? Some boards with similar hw layout has settings for JP-21. Thats why I tried whenn the original settings didnt work and still not working.

It just randomly boots, just shows blank screen other times. 1/10 maybe. Settings are correct.

1JP21
2
3 OOOOOO |         | OOOOOO        |  |  |
4 OOOOOO |         | OOOOOO        |  |  |
5 OOOOOO |         | OOOOOO        |  |  |
6 OOOOOO |         | OOOOOO        |  |  |
7 OOOOOO |         | OOOOOO        |  |  |
8XXXXXXXXXXX     XXXXXXXXXXX     XXXXXXXXXXX
9  1  2  3         1  2  3         1  2  3
10
11  66 MHz          83 MHz          100 MHz
12               will not work
13               (black screen)

That's what I meant with "removed".

mkarcher wrote on 2024-03-18, 09:25:

That's what I meant with "removed". […]
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fsinan wrote on 2024-03-18, 06:33:

Removed? Non-functional? Some boards with similar hw layout has settings for JP-21. Thats why I tried whenn the original settings didnt work and still not working.

It just randomly boots, just shows blank screen other times. 1/10 maybe. Settings are correct.

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1JP21
2
3 OOOOOO |         | OOOOOO        |  |  |
4 OOOOOO |         | OOOOOO        |  |  |
5 OOOOOO |         | OOOOOO        |  |  |
6 OOOOOO |         | OOOOOO        |  |  |
7 OOOOOO |         | OOOOOO        |  |  |
8XXXXXXXXXXX     XXXXXXXXXXX     XXXXXXXXXXX
9  1  2  3         1  2  3         1  2  3
10
11  66 MHz          83 MHz          100 MHz
12               will not work
13               (black screen)

That's what I meant with "removed".

JP-21 is open. Does not boot. Every other single cpu I put on this board successfully booted.

CoffeeOne wrote on 2024-03-17, 20:16:

And sorry, but with that kind of infos it's hard to give advices: You wrote: JP21 set to 1-2, it boots as DX4 at 66 => Yes, that […]
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fsinan wrote on 2024-03-17, 16:31:

Jp21 set to 1-2 it boots as dx4-S at 66Mhz. 2-3 setting boots at 66Mhz no change. […]
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Jp21 set to 1-2 it boots as dx4-S at 66Mhz. 2-3 setting boots at 66Mhz no change.

Cpuid reports are dx4 at 66mhz with 3x multplier.

Speedsys reports as 486dx4-66mhz. 16Lb cache.

When jp21 set to 2-3 then it does not boot as 100Mhz, black screen.
......

And sorry, but with that kind of infos it's hard to give advices:
You wrote:
JP21 set to 1-2, it boots as DX4 at 66 => Yes, that corresponds to the manual.
Then you wrote 2-3 setting boots at 66MHz. => 2-3 setting is not documented in the manual. I have no idea.
3 lines later:
When jp21 set to 2-3 then it does not boot as 100Mhz, black screen. => So what? 66 or black screen?

According to the manual it should be OPEN, so neither 1-2 nor 2-3.

But when the issue is solved, please ignore this post.

Maybe this jumper can not or does not register the config bit and does not matter what the setting is. Yes it is occuring like that. 1-2 boots 66, 2-3 boots 66 or black screen, open boots as 100 Mhz or black screen. SO my wiriting is ok. It seems there is something wrong with the mobo with Intel DX4-S