Yes, I believe it is a Cyrix core, however it has the 8k cache (WB) according to CPU world so it should perform much the same as comparable intel or AMD chips. I'm not aware of any incompatibilities with the Cyrix 486, I thought those came later with the 6x86 but would be interested to hear more. I haven't used a Cyrix 486 CPU since they were new, I had a DX/2 80 myself and can't say I ever had an issue even being on a VLB motherboard with both I/O and VGA on that bus. Will be interesting to hear what others who have more recent experience have to say on the matter.

I know that many sites do mention compatibility issues and I also saw a youtube vide few years back where OS/2 for example didn't work on a cyrix cpu.

I didn’t have any trouble getting OS/2 Warp installed on my Cyrix 486 Dx/2 66. I am now running WfW, Win95 and DOS 6.22 without a problem on it, also no problems with any game I tried to run on it.

Most issues with Cyrix CPUs was due to WB cache IIRC.

Cyrix was a fabless CPU designer, and they outsourced the production to other companies such as ST, IBM and TI. Normally as part of the deal they would allow the other party to sell Cyrix chips under their own label. Sometimes there were minor differences between them, such as die process (which affects heat production and overclocking potential) and in the case of the 5x86 different multipliers (2X/3X for IBM and 3X/4X for ST).

There were only very minor compatibility issues with Cyrix 486 CPUs, and I think normally patches or updates would have been released to resolve them if serious. My understanding is integer performance of Cyrix 486 is a little worse than Intel, while floating point is a little stronger.

I just saw some tests that would indicate that in doom timedemo cyrix with same clockspeed as intel or amd cpu would be about 15% slower compared to them. That might make 80Mhz cyrix to be about same speed as 66Mhz intel or amd one. Difficult to choose which one to use, but my 486dx66 isn't SX911 instead of SX955 one so it can't use WB cache.

Anonymous Coward wrote on 2020-02-10, 10:21:

My understanding is integer performance of Cyrix 486 is a little worse than Intel, while floating point is a little stronger.

Funny, I remember it being the other way around. Quake performance was definitely worse on my 6x86 than on my friend's P120 setup…

root42 wrote on 2020-02-10, 11:39:

Anonymous Coward wrote on 2020-02-10, 10:21:

My understanding is integer performance of Cyrix 486 is a little worse than Intel, while floating point is a little stronger.

Funny, I remember it being the other way around. Quake performance was definitely worse on my 6x86 than on my friend's P120 setup…

He is specifically talking about the 486 chips.. (though I was under the impression that the Cyrix 486 CPUs were marginally smaller than equally clocked Intel/AMD chips in both ALU and FPU calculations - I should test this sometime..)

The 6x86 is a 5th Generation CPU and yes it has significantly worse FP performance than AMD K6 let alone the Intel P54C..

To best compare the Cyrix to the Intel, you should run both at 66MHz in write-thru mode...and also make sure the Intel part is 5V, as the 3.3V version has an enhanced core.
...however, in the real world the Cx486 was normally run in write-back mode, and the intel in write-thru. Cyrix was an early adopter of write-back L1 cache. i486s with write-back cache were mostly during the Pentium era....and almost exclusively used in OEM systems.

I remember it being a hair slower than the i486 in non fpu based apps.
They were able to outperform i486 and am486 regarding memory transfers though.