I vote for neither. After some really long thinking about it and reading posts at VOGONS (valnar's post was the one that convinced me: 486), I decided to build my 486 around the Intel DX2-66. It's compatible with every board, it was popular in real 486s, and it should be enough for games tailored at the 486. Unless you build the 'ULTIMATE 486' I wouldn't use AM5x86 or DX4. The AM5x86 was meant rather as a upgrade CPU than a CPU for a new machine.

very interesting as I have both a 486/100 and 5x86/133 cpu... My mobo is of the latest isa/pci ones and supports both so I wonder what cpu to use... Would be nice to hear other ppl's experiences on the matter

These two are rather similar...
The AMD has faster clock speed, but this advantage is for the most part eaten up by the slow 486 system architecture (narrow memory bus, low FSB).
The Intel's better FPU performance doesn't help very much because only very few programs of that era actually use the FPU.
So, if you've got one of them, there is not much reason to get the other.

However, the Intel DX4 has one advantage: Its selectable multipliers are more convenient for retro gamers:

1CPU:         | Intel 486DX4 | AMD 5x86-P75
2Multipliers: |    x2/x3     |     x3/x4
3-------------+--------------+--------------
4 FSB 25 MHz  |  50/ 75 MHz  |   75/100 MHz 
5 FSB 33 MHz  |  66/100 MHz  |  100/133 MHz 
6 FSB 40 MHz  |  80/120 MHz  |  120/160 MHz

For playing old games, clocking down to 50 MHz makes more sense than running 133 or 160 MHz on a 486-class CPU.

So my vote goes to the Intel DX4. Or AMD DX4, but that one's not listed 😉

My favourite is the DX4 100 since the am5x86 doesn't always work in all socket 3 systems
The Intel DX4 100mhz CPU's have 16k L1 cache as the am5x86..imho the speed increase you get with the am5x86 isn't huge

the main question for us IMHO is: are there any games that really require 486/100 or 5x86 that won't run on a pentium1 system? Obviously a windows95 setup would benefit, but perhaps those cpus can cause speed problems and perhaps make the need for a high-clocked 486 machine just a "luxury"

keropi wrote:

the main question for us IMHO is: are there any games that really require 486/100 or 5x86 that won't run on a pentium1 system? Obviously a windows95 setup would benefit, but perhaps those cpus can cause speed problems and perhaps make the need for a high-clocked 486 machine just a "luxury"

It feels like a 486 is the sweet spot for 1993-94 games...later DOS games are often SVGA enhanced and needs at least a P75-90 to run at acceptable speeds
Prior to 1993 a 386DX 33 with cache is the sweet spot imho

So you're right....a P1 system is better to have than a hyped socket 3 system

Amigaz wrote:

So you're right....a P1 system is better to have than a hyped socket 3 system

That depends... some 386/486-optimised games do not work on Pentium-class (pipelined) CPUs, regardless of the clock rate.

Also, a high-end 486 board is one of the most versatile solutions, especially if you prepare it for quick CPU swaps (glue heatsink to CPU). For example, if a game runs to fast on the 486DX4, clock it down to 50 MHz. If it's still too fast, swap in a 486DX, clocked at 25 MHz. If that doesn't suffice, deactivate the L1 cache. Voilá, crawls like 386. And there's still that turbo switch to play with... 😉

I don't like Pentium1 machines much because of their limited speed/multiplier range. Better get a K6 for Socket7 systems, it goes all the way up to ~500 MHz.

5u3 wrote:

Amigaz wrote:

So you're right....a P1 system is better to have than a hyped socket 3 system

That depends... some 386/486-optimised games do not work on Pentium-class (pipelined) CPUs, regardless of the clock rate.

Could you provide some titles (for testing purposes, it would be nice to have a list of problematic games).

Games that deploy prefetch-queue tricks won't work on pentiums,
don't remember game titles, but Savage was one of them (pretty old one).

I think if you plan to run either chip in an older 5V only 486 board, the am5x86 is clearly the better choice in terms of compatibility. The am5x86 was at least designed to be somewhat of an upgrade chip, whereas the Intel DX4 pretty much required the updated platform. From what I understand, even when using a 5V to 3.3V a adapter, the Intel DX4 presents some incompatibilities related to the larger L1 cache. I have read that if the BIOS has not specifically been updated, you will only be able to utilise 8kb of the full 16kb cache. Of course, this issue probably does not affect the DX4 Overdrive part.

The Intel DX4 "&EW" writeback version should not be used in an older board at all because you cannot switch the caching scheme to write through. While the system will appear to work fine initially, you'll likely end up with cache coherency problems that result in a system crash at some point.

So in my opinion the am5x86 having the ability to toggle the L1 between writeback and writethru is a huge plus.

GL1zdA wrote:

Could you provide some titles (for testing purposes, it would be nice to have a list of problematic games).

Can't remember titles as well, and since I'm using this type of games on a real 486, I'd never notice these problems... 😊
However, the most prominent example is the first Comanche game, it needed a patch to work on Pentium systems.

Anonymous Coward wrote:

From what I understand, even when using a 5V to 3.3V a adapter, the Intel DX4 presents some incompatibilities related to the larger L1 cache. I have read that if the BIOS has not specifically been updated, you will only be able to utilise 8kb of the full 16kb cache.

But that would affect the AMD 5x86 too, since it also has 16KB L1 cache. Only the AM486DX4 CPUs have 8KB.

5u3 wrote:

GL1zdA wrote:

Could you provide some titles (for testing purposes, it would be nice to have a list of problematic games).

Can't remember titles as well, and since I'm using this type of games on a real 486, I'd never notice these problems... 😊
However, the most prominent example is the first Comanche game, it needed a patch to work on Pentium systems.

Wow, now I feel bad for steering GL1zdA wrong. 😮 I guess a 486 does have it's place.

I never tried Comanche on my Pentium, so I think I will. I've always ran it under DOSBox since I last played it on a 486 ages ago.

Isn't a Cyrix 6x86 more 486-compatible than Pentium? I wonder how one of those or a K5/6 would compare for compatibility.

Or maybe a Winchip or Winchip 2? Those aren't even pipelined designs.

valnar wrote:

Wow, now I feel bad for steering GL1zdA wrong. 😮 I guess a 486 does have it's place.

Well, only very few games are programmed in this way, and there are patches for the mainstream/common ones.
If you are into non-commercial software (like scene demos or independent games), you'll encounter this problem more often.

In the end it's just a matter of preference. DOSBox is always an alternative 😮

I had a 233mhz 6x86 from Cyrix back then... windows perfomance was awesome, but gaming one was terrible... 6x86 was meant to replace the pentium1(mmx) cpus so comparing it to 486 architecture is not fair
Plus IIRC the 6x86 had a large L2 cache (and ultra-weak FPU) so this can lead to troubles...

Well what I mean when I compare a Cyrix 6x86 to a 486 is that the 6x86 is missing Pentium instructions I believe. Either that or I'm thinking of PPro instructions which I'm sure it lacks.

Winchip is an awful lot like a 486. It's in-order. FPU stinks. It has MMX and 3DNow (Winchip 2) though and is a easy drop in for most mobos. 😀 I was kinda fasinated by Winchip 2. It even has 64K L1 cache. K6 is a better chip in general though.

been messing around with a 5x86/133 cpu.... I replaced my i486/100 with it, and facing some weird probs, like programs semi-crashing etc... I am doing a mem-check atm , will see how that goes... gonna replace it soon with the 486/100 again to see if same progs have the same behaviour
(using a soyo sy-4saw mobo, fully supports 5x86 cpu's)

Make sure your mobo supports write back caching otherwise the 5x86s can do weird things unless jumper them for write thru mode.

yeah, both BIOS and jumper is in write-back position.... 🙁