486DX does have a FPU (Floating Point Unit, or integrated math coprocessor). 486SX does not.

Now, here comes the question, which is better?

486DX for CAD, Excel, Quake and any other FPU-intensive program.

For everything else, they are equal if run at the same clock speed.

thanks, I'm just getting my sbpro sound card setup.

One last itsy bitsy question, cn I put the dx in the sx system and vise versa?

Sure, but expect DX to draw more power than SX. It may need better cooling.

EDIT: Bah, forget the last part. I don't think it will be an issue at all.

Just curious, what are the speeds of the two chips?

Don't they actually have the FPU, only it being broken?

Iirc the earlier ones were damaged FPUs but the newer ones were disabled.

nemesis wrote:

Iirc the earlier ones were damaged FPUs but the newer ones were disabled.

Why would they intentionally disable the FPU if it is good? They could sell that chip for more money as a DX if it works. I don't think Intel would do that unless there was a problem with the FPU.

sliderider wrote:

nemesis wrote:

Iirc the earlier ones were damaged FPUs but the newer ones were disabled.

Why would they intentionally disable the FPU if it is good? They could sell that chip for more money as a DX if it works. I don't think Intel would do that unless there was a problem with the FPU.

It's quite common for cpu manufacturers to do this in order to meet demand. I imagine that with the 486 this sort of thing would be more common in the early phase of its life - probably 25-33Mhz range - a lot of people wouldn't want to pay for floating point features when they didn't need them.

Motorola were notorious for it with their 680x0 series which had various models with and without floating point and memory management units. The circuitry was all still on the die, but either faulty or actually just electricaly disabled. You could sometimes get both features enabled if you had a chip were they had been disabled but were intact.

I believe they are both 33mhz

If they're both 33MHz, then they will be exactly the same speed as each other for 99% of the software and games that were available when the 486 was on the market. There will be rare occasions when a game can detect and use the math coprocessor of the DX (eg some flight sims, Quake [but not Doom or Duke 3D], some Windows applications), in which case it will be faster, but in all other situations the speed will be identical.

Well, since they are the same speed, will the dx give me more compatibility?
Because some games specifically call for a math coprocessor, so if I have that then will I have a higher chance of being able to play more ms-dos early gen games?

I doubt it will do anything for compatibility. Early games are less likely to need an fpu though - it's really only going to be later 3d, games that will benefit.
You may as well use the DX if you've got one, it's shouldn't stop anything running.

K, I'll swap them out. I'm just trying to get the highest compatibility I can.