First, 386-40 is not that far from your 486sx in terms of performance, there is of course variance depending on the cache, graphics card etc., but although 486SX-25 is faster, the difference isn't most likely huge.

386SX-25 is or should be roughly double as fast as your 286, so there is already quite a big difference. Then again, I wouldn't worry some "gap" between 386SX and 486 systems because when you find 386SX struggling, why don't you just use some of your 486 systems to run the software?

If your SX is not soldered, you could try to get an AMD 386SX@40 so you could get a speed comparable to a lower spec 386DX (to get things more balanced). If it's soldered, I'd keep it as-is. Disabling caches and de-turbo 486s would give you performances on par with 286 and 386... so I think your "gap" is already filled.

You could try swapping crystal/clockgen chip for 66MHz one. Intel was manufacturing 25 and 33 chips on same process.
Not that it will make much of a difference for your situation, as it sounds like you already have excellent if not excessive speed coverage with other systems.
There arent really that many speed sensitive games, and I dont think any of them would somehow fall in a crack between 386sx-25 and 486SX-25.

CharlieFoxtrot wrote on 2023-10-21, 09:00:

First, 386-40 is not that far from your 486sx in terms of performance, there is of course variance depending on the cache, graphics card etc., but although 486SX-25 is faster, the difference isn't most likely huge.

386SX-25 is or should be roughly double as fast as your 286, so there is already quite a big difference. Then again, I wouldn't worry some "gap" between 386SX and 486 systems because when you find 386SX struggling, why don't you just use some of your 486 systems to run the software?

Yes, that's what I'll do, that is, when a software works slowly I move up to a higher CPU class. I was just wondering if the only 386 I own is a valid representative of the 386 category

AlessandroB wrote on 2023-10-21, 09:38:

CharlieFoxtrot wrote on 2023-10-21, 09:00:

First, 386-40 is not that far from your 486sx in terms of performance, there is of course variance depending on the cache, graphics card etc., but although 486SX-25 is faster, the difference isn't most likely huge.

386SX-25 is or should be roughly double as fast as your 286, so there is already quite a big difference. Then again, I wouldn't worry some "gap" between 386SX and 486 systems because when you find 386SX struggling, why don't you just use some of your 486 systems to run the software?

Yes, that's what I'll do, that is, when a software works slowly I move up to a higher CPU class. I was just wondering if the only 386 I own is a valid representative of the 386 category

I don't see why one CPU would be more represetantive over any other. Yes, SX isn't a full 32-bit 386 processor like DX because of the 16-bit external bus, but they were nonethless very common processors for a couple of years in the late 80s and early 90s and paved a way for low cost 32-bit computing. They perform worse compared to DX, but they are still decent systems for the era even though they are on par clock-to-clock with 286.

How exactly were you planning to upgrade a 386SX (with 16b bus) to a 386DX or 486 (with 32b bus)?

It's a completely different ballgame, as if you were to try to upgrade a 486 to a Socket 4 or 5 Pentium (and yes, there were a couple of Frankenstein boards that could do both (badly), so probably there were some SX/DX boards too - if you have one, it could be very sought-after).

FIrst question is if the CPU is soldered (already asked, not answered). If it is, you need SMD skills to do anything. The fastest 16b bus CPUs are the 486SLC and 486SRx CPUs from Cyrix and IBM. The IBM units were fastest, clocked up to 66MHz, but due to legal issues with Intel, they were never sold as separate CPUs. Cyrix did sell theirs, so that is practically speaking the fastest you could attempt.

Of course, discrete 486SLCSRx CPUs are rare as hens' teeth, and if you need to buy a board with one on it, you might as well use that board instead.

There used to be some upgrade chips:

I didn't specify but considering that I also collect these IBM computers I don't want to modify them in any way by desoldering the CPU or the oscillator. I was thinking of something like a chip-on-chip with something like a 386sx40mhz but without installing a 486lc or anything like that, I would like to have a genuine 386 without going into 486 territory. The 386sx25 is soldered onto the mainboard. My little doubt is whether the 386sx was considered a "real" 386 and whether at 25 MHz it could fit in between my 286 and the slowest of my 486s.

Definitions... the core is a very real 386 32b core with i386 instruction set, the bus is an equally real 16b bus with commensurate 16MB RAM limit.

In terms of performance, a 286 can frequently outperform a 386SX clock-for-clock, but obviously can't run 386 code natively. If running 32b code, you need the 386 and a 386SX is one. If running 16 code, it doesn't add huge value over a 286 at similar speed unless it runs significantly faster or has other benefits like VLB slots.

I personally find not having to worry about whether $program has any 386 instructions a significant benefit, and I'm actually more likely to get rid of my 286 than either of my SLCs (an IBM SLC2-66 at home and a Cx486SLC in a tiny case at work for DOS games when we hang around after hours for drinks and fun). For tinkering with really old stuff my XT beats 286 hands down anyway.

Thank you for your always extremely technical and competent answers, mine is more of a request for "field" use of a 386sx25. I'll give you an example, I already knew, but you confirmed to me, that having a 386dx40 and a 486sx25 is very similar as a 360 degree result in the game. so having a 386dx40 and a 486 on socket like I have makes little sense. For example, I played a bit of Wolfenstein on the SX25 and I found it very stimulating in its slight jerkiness and in the use of the integrated buzzer for the audio (I then also used it with an sbPro2 with great satisfaction for the ears and for my memory)