486SX makes a great DOS gaming machine. The lack of co-processor isn't a big deal.

Very very few games from the period benefited from the FPU as they were integer dependent but hordes of people bought the DX thinking they would be getting better performance.

Co-processor doesn't become super relevant for games until the Pentium era and Quake. Phil made a video comparing the 486SX-25 to the 386DX-40. 486-25 comes out ahead by more than you would think. 486-20 is probably closer to 386-40 speed.

https://www.youtube.com/watch?v=3fcPxAO1FeU

BTW, 386DX doesn't come with a co-processor, either. The difference between the 386DX and SX is the width of the memory bus. DX uses a 32-bit memory bus while the SX uses a 16-bit bus. The SX was made that way so that motherboard manufacturers could reuse their 286 motherboard designs with only a modification for mounting the 386SX. 286 motherboards had become cheap to make near the end of their life and the 386SX allowed Intel to leverage their way into the cheap PC market.

Whether a 486SX 25 is a great DOS game CPU or not depends a lot on the game selection. It isn't going to be much fun with games beyond 1992/1993. This was the 486 budget box favorite.

As everyone else said, copros don't matter until ~1996. Games that really need copros don't run very well on any 486-class CPU.

No Quake, that matters a lot to me :p

nforce4max wrote:

Very very few games from the period benefited from the FPU as they were integer dependent but hordes of people bought the DX thinking they would be getting better performance.

Well, in the early days the DX was also available at higher clockspeeds, I believe.
When I got my DX2-66, I don't think there was an SX2-66 alternative. Only 25 and 33 MHz models, if I'm not mistaken. It was the 'Celeron' of its day.

The FPU isn't very relevant for 2 reasons:
1) In the early days of 486, games had to be compatible with 386 as well, so most games would not use an FPU. I know of only one game from that era that can optionally use the FPU, and that is Falcon 3.0.
2) The FPU in the 486 wasn't very fast. For a lot of calculations, fixedpoint arithmetic on the CPU was faster than using the FPU. So even when games targeted the 486 specifically, they would generally not use the FPU. Which is also why Quake runs so badly on 486. It uses the FPU, but it is aimed at Pentium 75-90, which has a much faster FPU than a 486. So even a 486 running at 133 MHz or above won't get close to that level of performance.
Descent uses a graphics engine with similar capabilities to Quake, but aimed at 486, and not using FPU.

computergeek92 wrote:

I've read that a 486SX 20MHz is about equal to a 386DX 40MHz but with no co-processor. How does lacking that impact games of that era? I personaly own a 486SX 25 PC i'm trying to get working but have run into IRQ errors but how good is the performance? It has 4MB of 30 pin simms and a 425mb hdd, plus a 256k VGA card taken from a 286 PB.

With this configuration I wouldn't bet you'll get an average 386DX-40 performance. With the wrong VGA card you can even get slower results then average 386DX-20.

When I upgraded my computer in 1993 from 286-16 to 486slc-33, I didn't change the 256KB VGA card. The performance in games was rather disappointing. Only after I swapped it for a _speedy_ Trident 8900D 🤣 I got a performance boost of a 486slc.

Recently I did some benchmarks with different Trident 8900 cards and got quite mixed results. From very slow to very fast - comparable to Tseng ET4000. In 3DBench results were from 23 to 48fps on 486DX4-160.

I know Simcity 2000 will use the FPU. For some reason I thought warcraft might, but I think I'm wrong.

kixs wrote:

With this configuration I wouldn't bet you'll get an average 386DX-40 performance. With the wrong VGA card you can even get slower results then average 386DX-20.

It could also work out very well 😀
When I upgraded to a 486, I re-used the Western Digital ISA card from my 386SX-16 at first. This card was much faster than the common Trident, Oak or Realtek ISA cards you'd find in most 386/486-clones.
Some 286es may actually have some really speedy ISA cards 😀

It might but I guess it would have more than 256KB of ram 😉

kixs wrote:

It might but I guess it would have more than 256KB of ram 😉

Not necessarily.
The WD card I had was 256KB standard as well. I upgraded it to 512KB myself.
But for regular 320x200 games, there's no point in having more than 256KB anyway. It was only for enabling higher resolutions/more colours in Windows.

I have a 486SX at 33mhz. Don't bother playing games beyond '94. It's quite dissapointing. 😊 The only game that I was interested in, that didn't get performance issues was Monkey Island. Doom was only playable in low graphics and mega small 'screen size'. In my opinion, to get the best of (and most varied experience under one hood) what the early to mid/late 90's has to offer the solution is a Pentium.

Blurredman wrote:

Doom was only playable in low graphics and mega small 'screen size'. In my opinion, to get the best of (and most varied experience under one hood) what the early to mid/late 90's has to offer the solution is a Pentium.

Sounds like a bad videocard issue.
I had a 486DX2-66 with VLB (0 waitstate), and it ran Doom extremely smoothly, at full screen and high detail. Theoretically a 486SX2-66 with VLB should run just as fast, since the FPU is the only difference, and it's not being used.
A 486SX-33 should still get more than half the speed of a 66 MHz machine, so it should still play Doom quite nicely, if it's not bottlenecked by a slow videocard.

Scali wrote:

When I got my DX2-66, I don't think there was an SX2-66 alternative. Only 25 and 33 MHz models, if I'm not mistaken. It was the 'Celeron' of its day.

Yes there was: http://mail.lipsia.de/~enigma/neu/pics/486SX2-66.jpg
It is only slightly slower than a DX at integer calculations, max. -10%.

elianda wrote:

Scali wrote:

When I got my DX2-66, I don't think there was an SX2-66 alternative. Only 25 and 33 MHz models, if I'm not mistaken. It was the 'Celeron' of its day.

Yes there was: http://mail.lipsia.de/~enigma/neu/pics/486SX2-66.jpg

Not back in ~1992 I think.
According to this page, it was introduced in 1994: http://en.wikipedia.org/wiki/Am486
The DX2-66 was introduced in 1992: http://en.wikipedia.org/wiki/Intel_80486
So at the time I bought my 486DX2-66, there was no SX2-66 on the market yet, as I said. Intel was the only one to offer SX models back then, and they only went up to 33 MHz.

elianda wrote:

It is only slightly slower than a DX at integer calculations, max. -10%.

Why would it be slower at integer at all? It is exactly the same CPU, so if you run it on exactly the same motherboard, with exactly the same settings, integer performance should be exactly the same.

swaaye wrote:

Whether a 486SX 25 is a great DOS game CPU or not depends a lot on the game selection. It isn't going to be much fun with games beyond 1992/1993. This was the 486 budget box favorite.

As everyone else said, copros don't matter until ~1996. Games that really need copros don't run very well on any 486-class CPU.

For any game developed after 1993 I would say rather opt for a very fast 486 (DX4-100 or higher) or, even a Pentium 1.
However, some older DOS games were "speed sensitive" (as some of these came out before 486DX2 CPU's even existed and game developers didn't always take the speed increase into account). Fortunately, most 486 and early Pentium 1 motherboards had the functionality to slow down the CPU via the turbo switch button in the front of the case (provided that it was properly connected to the motherboard).

The 486slc I had in 1993. Really sucked at games from 1993 and onwards.
On the other hand, it was a really shitty repack of the 80386 cpu.

Scali wrote:

elianda wrote:

It is only slightly slower than a DX at integer calculations, max. -10%.

Why would it be slower at integer at all? It is exactly the same CPU, so if you run it on exactly the same motherboard, with exactly the same settings, integer performance should be exactly the same.

The SX requires more cycles for memory fetches due to reduced bus width. The 486SX takes an additional cycle for every additional opcode with a size greater than 16 bit. So a 4 byte opcode takes +1, 5 or 6 byte opcode +2 cycles.

I recommend the book Microsoft's 80386/80486 Programming Guide by Nelson, Ross P. (ISBN 9781556153433)

elianda wrote:

Scali wrote:

elianda wrote:

It is only slightly slower than a DX at integer calculations, max. -10%.

Why would it be slower at integer at all? It is exactly the same CPU, so if you run it on exactly the same motherboard, with exactly the same settings, integer performance should be exactly the same.

The SX requires more cycles for memory fetches due to reduced bus width. The 486SX takes an additional cycle for every additional opcode with a size greater than 16 bit. So a 4 byte opcode takes +1, 5 or 6 byte opcode +2 cycles.

I recommend the book Microsoft's 80386/80486 Programming Guide by Nelson, Ross P. (ISBN 9781556153433)

Answers like this are what makes VOGONS great. *thumbs up* 😁