i suggest you to get a amd5x86-133, its the fastest 486 kernel(excluding the pod and cyrix5x86 which are 586 kernels stuffed into a 486 package).
ti, st and ibm are all rebranded cyrix.
integer performance: intel>>amd>cyrix
floatpoint performance: amd>intel>cyrix

AMD for raw clocks, Cyrix 5x86 for performance per clock, Intel because it is Intel, and Ti because it is different. All the above are worth collecting and are a lot of fun to play with.

The AMD and the Ti are the cheapest while the Intel can get pricey but you can kinda cheat on the Cyrix but condition is almost always poor. Eastern Europe has a few on eBay here and there for less than $20 but it is a risk if they even work but they won't show under some searches. I got my Cyrix 5x86 for $12 shipped here in the states that was sold as is but it turned out fine after dealing with the pins.

Grab whichever is easier to get, there's not a whole lot of difference there.

Agree with the other posts. However, check which CPU's your motherboard supports.
My Asus motherboard (same model number as yours) only has BIOS revision 0305, which doesn't support the later AMD & Cyrix CPU's.
There were, however, later BIOS revisions supporting the AMD5x86 & Cyrix CPU's but, it's not a "flashable" BIOS, meaning you need an EEPROM burner to "burn" a new BIOS.

If you are strictly looking at a 486DX4-100, then the Intel is your best option, since (based on my understanding) the Intel 486DX4-100 CPU's had a 16 KB L1 cache from the start.
Both the AMD & Cyrix CPU's started out with 8 KB of L1 write through cache, but AMD did later on add a CPU with 16 KB of L1 write back cache. The former is more common.

You can refer to http://www.cpu-museum.de & http://www.cpu-collection.de for more info.

so am i right to think that going from DX2 80mhz ->>> DX4 100mhz is worth it?

or might as well get CYRIX ?
http://www.ebay.ca/sch/i.html?_odkw=cpu+cyrix … 86+mhz&_sacat=0

i did this search. it only shows 100mhz Cyrix chip? is that the one to get?
people overclock it to 133? and the 133 to 160?

Cyrix 5x86 doesn't overclock well. 100MHz would probably work at 120 but 133 is usually too much. Over 133 you have to be darn lucky. But AMD 5x86 overclocks well... from 133 to 160 and if you're lucky even more. But performance wise Cyrix 5x86 is quite faster than AMD 5x86.

Is TI exactly the same as Cyrix? I suspect there are some differences. TI and Cyrix had a falling out over the 486DLC, and I believe all of TI's CPUs produced after that point were based on Cyrix designs modified by TI engineers. Is there anyone who knows for certain what happened?

The 486SXL was the CPU that ended the TI/Cyrix relationship because TI illegally modified the 486DLC to accept 8kb cache (so it is said). That particular CPU was produced for both 132-pin and 168-pin packages. I am going to speculate that all future TI 486 CPUs were based off the 486SXL. I believe Cyrix basically followed the same path with their 486S and 486D chips, but I am really curious how TI went about incorporating the FPU into their 486 chips. Did they have access to the fasmath design, or did they design their own?

Rumour has it that TI was also working on their own 5x86 CPU. Whether it was a turbo charged 486 like am5x86 or a completely new design like cx5x86 is unknown as TI exited the x86 CPU market before it was ready for sale. Apparently prototypes exist. I believe there is a Chinese CPU collector who has one, but I was unable to get his name. The chip was originally sold on cpumuesum, but the seller is still active on cpu-world.

If you go for a DX4-100, then Intel is a safe bet, because they all have 16KB write-back cache, the best possible configuration.
With AMD, there's both 8KB and 16KB variations. The 8KBs will be slower than the Intels. Not sure if the 16KB are as fast as Intel, but probably close enough. So you have to be careful which one to get.

Dude just stick with your dx2 80mhz if it is stable. Snag an Pentium Overdrive if you are going to upgrade! That is what would really be worth it.

Scali wrote:

If you go for a DX4-100, then Intel is a safe bet, because they all have 16KB write-back cache, the best possible configuration.
With AMD, there's both 8KB and 16KB variations. The 8KBs will be slower than the Intels. Not sure if the 16KB are as fast as Intel, but probably close enough. So you have to be careful which one to get.

All have 16kb, but aren't many of them actually WT? It was my understanding only the &EW models support write back.

Anonymous Coward wrote:

All have 16kb, but aren't many of them actually WT? It was my understanding only the &EW models support write back.

You're right, the earlier 'P24C' models are WT, the later 'P24D' ones are WB.

Scali wrote:

You're right, the earlier 'P24C' models are WT, the later 'P24D' ones are WB.

The intel DX4 '&EW' Write-Back model can do Write-Through mode as well. They are dual mode. Come with 16kB of course.
The AMD DX4s usually have 8kB cache, where the last part of the product code is 'SV8T' meaning 8 kB Write-Through. But for example you can find 'SV16B' too, meaning 16 kB Write-Back. Not sure if the latter are also WT capable (probably yes). These product codes are from the final AMD socket 3 line-up, where they adjusted their pinout to match the intel DX4.
The above mentioned DX4 CPU's can be jumpered to run 2x speed or 3x speed (default). But some later AMDs like their Am5x86 / X5 are 3x and 4x instead.
The normal Cyrix Cx5x86 can be jumpered at 2x speed or 3x speed (default), but in addition SetMul software can make it run 1x speed. That 1x is the killer feature for me personally. There are some rare Cx5x86s that go faster.

(When I talk about these speeds I mean 1x33=33MHz / 2x33=66MHz / 3x33=100MHz / 4x33=133MHz.)

Cheapest bet is the amd 5x86 133mhz. Just clock it at 100mhz or clock it as high as you like later (up to 160mhz). It is for sure the 16kb amd and is wb. At 100mhz it is exactly the same speed as an intel dx4-100.

Cyrix 5x86 100Mhz is the fastest of the bunch - especially if you enable 6x86 instructions. Then there's the AMD 5x86-133 P75 - these can be overclocked to 160 Mhz on some motherboards - then there's the 100MHz Intel and AMD DX4 cpus. Go for the 16kb / WT models. I recommend the Cyrix.