None of them has a math-co processor... (You need a 387 separately)

SX has 16bit wide bus, DX has 32bit wide bus.

The DX is faster than the SX at the same speed, not the other way around. Not by far though.
Max memory for an SX is 16MB, again, not something you should really be worrying about.
The DX doesn't "have" a 486-style coprocessor. But if the m/b permits it you can add one to both the SX and the DX.

The 386SX was basically a low-cost version that could be installed on a 16-bit 286-style motherboard/chipset. It's similar to the 8088 vs 8086.

Very few SX boards have cache. An SX without cache is about half the speed of a DX with cache, particularly at 33 and 40MHz.

My 386SX 25 without is as fast, if not faster than one of my friend's 386SX25 with cache. My bios lets me lower the timings really low. In fact, it's so low my 386DX40's RAM not super faster : my SX25's RAM bandwidth is 13MB/sec and my DX40's bandwidth is 20MB/sec. Since the DX is running 1.6 times faster and that the bus' width is twice as big, then the thing should be nearly 3 times faster, isn't it ? But nope, it's just 1.6 times.

My bet is that my SX communicates with its ram at 25MHz and runs at 25MHz while my DX communicates with its ram at 20MHz and runs at 40MHz.

So if I'm correct, I think cache for the SX is just meaningless in that case, while my DX has 64KB of cache to avoid loosing too much performance due to slow RAM.

I think you can actually have a SX being as fast as a DX if your ram runs twice as fast as the DX' to counterweight the bus being 16 bit instead of 32 bit (though I doubt you can find simms that can run that fast).

Actually, I'm curious to see a Speedsys benchmark being done on a 386DX25 ^^

Intel486dx33 wrote:

What are the benefits of a 386sx-40 vs, 386dx-40 ?
Besides the obvious that the DX has a math-co processor

This is one of those misconceptions that will never die. As people have pointed out before, the difference is not FPU-related. SX means Single word external, or having a 16-bit external data bus; DX means Double word external, or a 32-bit external data bus. The original 386's didn't have the DX or SX nomenclature; it was introduced with the 386SX which was released after the original 386. With the exception of the RapidCAD, the FPU for the 386 was external, in the form the 387 (in both DX and SX variants), or the 287 (it took 2 years after the introduction of the 386 for the 387 to appear).

Also, the SX has only a 24-bit address bus, so can only address 16MB of RAM vs 4GB for a DX, which has a 32-bit address bus.

Overall, you're going to have a better time with the 386DX than with the SX.

(Edited to clarify that the 387 wasn't the only FPU usable with the 386)

AlaricD wrote:

Intel486dx33 wrote:

What are the benefits of a 386sx-40 vs, 386dx-40 ?
Besides the obvious that the DX has a math-co processor

This is one of those misconceptions that will never die. As people have pointed out before, the difference is not FPU-related. SX means Single word external, or having a 16-bit data bus; DX means Double word external, or a 32-bit data bus. The original 386's didn't have the DX or SX nomenclature; it was introduced with the 386SX which was released after the original 386. With the exception of the RapidCAD, the FPU for the 386 was the 387 (in both DX and SX variants).

Overall, you're going to have a better time with the 386DX than with the SX.

287 and 287XL FPUs will work with 386 (in fact there were time, when they were only FPUs available for 386).

HanJammer wrote:

287 and 287XL FPUs will work with 386 (in fact there were time, when they were only FPUs available for 386).

True. And in the two-year wait for a 387, a 287 is better than nothing!