Downclock to 200MHz?

Oh, I mean 25mhz. or 33mhz.

How about just buy an 486dx33 or 486sx25? They are still affordable enough to get these days.

brostenen wrote:

How about just buy an 486dx33 or 486sx25? They are still affordable enough to get these days.

I would like the versatility of being able to run at a normanl speed of 100mhz or 133mhz and be able to downclock to 25mhz or 33mhz.
Is it possible ?

Which CPU is bests for this ?

Intel486dx33 wrote:

I would like the versatility of being able to run at a normanl speed of 100mhz or 133mhz and be able to downclock to 25mhz or 33 […]
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brostenen wrote:

How about just buy an 486dx33 or 486sx25? They are still affordable enough to get these days.

I would like the versatility of being able to run at a normanl speed of 100mhz or 133mhz and be able to downclock to 25mhz or 33mhz.
Is it possible ?

Which CPU is bests for this ?

If it can be downclocked, then it will work. I don't think you will destroy it. Test with the 5x86 first.
The biggest issue that you will have, is that you need to set the jumpers manually.
Or just build some kind of external switching.

How are you going to get down to 33MHz? Those CPUs don't have a 1x multiplier (unlike Cyrix 5x86 for instance). Unless your bus speed goes lower than 25, then the best you could do would be 50 or 75MHz and then disable the L1 cache.

Since you need to fiddle with jumpers anyway to downclock the CPU, might as well just switch to another CPU when required.

You could use the Reset switch on the case connected to an appropriate jumper on the board to change CPU type from DX2 to DX, which would theoretically disable the internal multiplier and bring the CPU down to 33Mhz.

As it was mentioned before, DX2 CPUs can't disable the internal multiplier.

The Serpent Rider wrote:

As it was mentioned before, DX2 CPUs can't disable the internal multiplier.

Then why do many boards have a DX/DX2 CPU type jumper?

appiah4 wrote:

The Serpent Rider wrote:

As it was mentioned before, DX2 CPUs can't disable the internal multiplier.

Then why do many boards have a DX/DX2 CPU type jumper?

The single multiplier pin on a 486 is ignored by most cpus

My AST Advantage 4/66d Cyrix had about 15 cpu jumpers and to move from a Cyrix to an AMD 5x86 I had to change them, I still ended up at 100mhz but at least it worked.

No idea what they all did, most 486 systems had voltage, a multiplier and one more jumper and that was it, they were all different

appiah4 wrote:

The Serpent Rider wrote:

As it was mentioned before, DX2 CPUs can't disable the internal multiplier.

Then why do many boards have a DX/DX2 CPU type jumper?

Incidentally, I was just going over the jumper settings for my Chicony CH-471A (rev.3) motherboard.
In many instances, you'll notice that the jumper settings for, say, an Intel 486DX-33 is the same as for an Intel 486DX2-66 and again for a 486DX-25 & a 486DX2-50.
I think motherboard manufacturers just listed each supported CPU's jumper settings separately to avoid users setting up those CPU's incorrectly.

Thanks All.
I have an IBM PS/1 with 486sx33 that was going to upgrade to 66mhz. But I think I will keep it at 33mhz now.

I am going to try out both of these CPU’s and see how low they will go.
I am going to use the “Setmul” program to disable L1 cache and use the turbo button function.