Previously I had written a post on pushing the limits of Socket 7 in this article. This time I’m going to explore pushing the limits of one of my favorite motherboard’s, the socket 3 board. Socket 3 motherboards were designed for the 486 CPU and represent a golden age of DOS from the early to mid-1990’s. Its no wonder then why many Retro computer enthusiasts cherish and focus on this era of PC gaming. As a matter of fact individuals attempting to see how far they can push the limits of motherboards meant for the venerable 486 is a rather popular topic in the hobby.
before I get into the article I want to point out that Feipoa, a user over at the Vogons forum wrote a very in-depth and well-researched post on the subject titled The Ultimate 486 Benchmark Comparison. The point of this article though is to not only perform my own benchmarks and come to my own conclusions but to try and express the results in a simplified manner. As awesome and well done as the Vogons post is it is a little bit lengthy and technical and may come off as a bit overwhelming to a retro PC novice or casual user. Hopefully this article will be user-friendly and straight forward enough for the retro PC newbie as well as maybe even make for a good read to a more experienced PC user. I do encourage readers to check out the link above though if you want to read further on the subject.
First off were obviously going to need a socket 3 motherboard. In general if you’re pushing the limits of socket 3 your going to want late model boards and this means motherboards with PCI slots. PCI slot 486 motherboards can be expensive and in some cases buggy as manufacturers hadn’t completely figured out the PCI standard but it’s really your only choice for getting the most out of the higher end 4×86/5×86 CPU’s as it offers the most options in BIOS, CPU type support as well as allowing much higher speed PCI video cards to take advantage of the fast CPU.
For my testing I used a Shuttle-HOT 433 motherboard. These boards are known to be a little buggy but support a wide array of faster 486 and 586 CPU’s at higher front side bus settings.
For all tests I’ll be using this motherboard. I’m running 32MB of FPM RAM, 512kb 15ns l2 cache, 0 wait states with a memory timing of 2-2-2 and for the video I am using a PCI Matrox G200.
As a baseline CPU I’m using the Intel DX2 66mhz. I’m using this CPU as a baseline as it represents the quintessential 486 of the mid 90’s and was a widely used, capable and popular gaming CPU.
Write-Back and Write-through memory
I also want to take a minute to talk about Write Back and Write Through memory. Starting from the 66mhz DX2 you start to see variants of chips using “Write-Back” cache such as this 66mhz DX2 below. The SX955 designates this CPU as the write-back variant.
Without getting technical this type of memory is faster than standard “Write-through” memory. Generally you need to enable write-back via the BIOS configuration screen else it simply acts as write-through. The option should be available in most late socket 3 boards and look something like this.
In my personal experience I haven’t noticed a huge performance jump using write-back but if you’re trying to get every ounce of performance it’s something to keep in mind. There are a few caveats to using write-back and that’s possible issues with stability much like with early EDO RAM usage. The other issue is most if not all VLB SCSI cards are incompatible with write-back settings. This means if you plan on using a SCSI VLB card for a hard drive or CD-ROM drive your not going to be able to enable write-back cache as well. I believe I have read this has to do with bus mastering conflicts. I have read some SCSI controller cards may be compatible or have a jumper that needs set to enable compatibility with write-back cache but that is unconfirmed by myself.
High end socket 3 CPU choices
Alright, now let’s talk about your choices for a fast high-end CPU in socket 3 format. You actually have about three choices and that comes down to the Intel route the AMD route or the Cyrix route. They each have their own positives and minuses and each tackles the situation differently.
AMD 5×86
Will start by looking at the AMD 133mhz 5×86 CPU.
This is the most common solution for turbocharging a socket 3 platform. The AMD 5×86 is fairly common and cheap. The name 5×86 is a bit of a lie though as this chip doesn’t have much in common with the other socket 3 5×86 chips were going to look at and is much more of a traditional 4×86 CPU. AMD’s approach was simply to turbocharge the 486 CPU and in this case they did very well. the AMD 5×86 is perhaps the mature height of the traditional 486 CPU. The image above is of an older variant that states that it requires heatsink and fan but later chips running cooler lack this requirement (though you probably should do it anyways). All AMD 5×86 chips regardless make excellent overclockers and can be overclocked to 160mhz fairly routinely by setting the front side bus to 40mhz. The AMD 5×86 at 133mhz is about equivalent to a 75mhz Pentium in speed (but not FPU functions). Overclocked to 160mhz it hovers more around a Pentium 90mhz in performance which is a significant speed boost for a socket 3 chip. remember a Pentium is superior in speed even when operating at the same clock frequency so a true Pentium 100mhz will blow an Intel 486 DX4 at 100mhz away. This chip overall is very compatible with socket 3 boards and generally runs very cool and stable even at 160mhz. I have read about a few instances of this chip being overclocked to 200mhz but this should be considered pretty advanced and nonroutine so is beyond the scope of the article.
The AMD 5×86 was produced for some time so labeling on the CPU itself differs depending on when it was made. On the far right is a later release of the chip with a year 2000 date code. Users have stated that they had better luck overclocking ADZ chips as opposed to the ADW labeled chips.
Cyrix 5×86
Next we have the Cyrix 120mhz 5×86 CPU
The Cyrix CPU is actually the polar opposite of the idea behind the AMD 5×86. Where the AMD chip takes a 486 and turbo charges it the Cyrix 5×86 takes their next generation 6×86 CPU and cuts it down disabling features to make it run stable on a socket 3 board. The Cyrix 100mhz chip is very common but the 120mhz chip as seen above is pretty rare. I was able to attain mine by luck off eBay about a year ago but have not seen any pop up since. There is also a 133mhz Cyrix 5×86 but this chip is very rare and for awhile it was doubted if it was even actually produced. Being that the 133mhz chip is rather unattainable we won’t be considering it for this article.
Unlike the AMD chip the Cyrix chip needs a little work to reach its full potential as programs can be obtained to re-enable some of the features that Cyrix disabled to help with stability issues. Re-enabling some of these features produces speed increases but in turn you may suffer stability wise. The only known motherboard to have built-in options to re-enable some Cyrix chip features (LINBRST and LSSER) is the infamous M919 motherboard otherwise you need to download and execute a program to reactivate these features. More information on these features and programs can be found here. I used the Peter Moss utility with my Cyrix chips and used these settings loop_en=off, rstk_en=on, lsser=off, fp_fast=on, btb_en=on while still achieving stability. your mileage may vary.
If you can’t find a 120mhz Cyrix chip there is still hope as IBM manufactured The Cyrix 5×86 under license. Due to IBM’s superior fabrication plants they were able to produce many chips rated at 100mhz that easily overclock to 120mhz. This is the chip I used for the benchmarks in this test.
Though uncommon these chips turn up on places like eBay far more then the Cyrix branded 120mhz chips and many of them are easily able to overclock to 120mhz like the one above. Note that you probably will not have the same success in overclocking the Cyrix branded 100mhz 5×86 chips that seem to be common on eBay. A number of the IBM 5×86 chips may even overclock to 133mhz but mine did not and this is to considered less likely a case than not. Results with a 120mhz overclocked IBM chip should be equivalent to a true 120mhz Cyrix chip.
Intel Pentium Overdrive
Finally we have Intel’s offering which is a paired down Pentium processor modified to work in a socket 3 slot.
This chip is possibly the most technically advanced of the upgrade paths but also the lowest clocked chip of the bunch coming in at 83mhz. I’ve read Intel tried to get a faster chip out there but ran into to many issues. You can overclock the Pentium Overdrive to 100mhz but it is not advisable. In my research most sources advised not to overclock the overdrive as it is a poor overclocker and is likely to damage the chip. For this reason the overclock should not be seen as routine so is not relevant to this article.
Despite the overdrive being restrained by the socket 3 architecture tests by HighTreason, another Vogons user, has shown that the 83mhz overdrive still outperforms a true Pentium 66mhz on a socket 4 motherboard in most tests. In my own comparisons benchmarks the Overdrive and Pentium 66 were fairly neck and neck each beating out the other in about half the bench tests but then I wasn’t using comparable video cards and such.
One advantage of the overdrive over the competition is its much superior floating point math processing in comparison to the AMD and the Cyrix. Its ability to take advantage of applications with optimized Pentium code is also a huge boon in some games and apps. Will see how this takes effect in the benchmarks.
The unrepresented chip
The one chip I wanted to include in testing but never got around to was Intel’s 100mhz DX4 if only because this was Intel’s last 486 chip. I doubt this chip would add too much to the tests though as its probably about equal to the Cyrix 100mhz 5×86 and a little faster than AMD’s 100mhz 486.
Benchmarks
And now that we’ve talked about the CPU options it’s on to the Benchmark tests. For the tests I’m using Phil’s benchmark’s which is a collection of four benchmark tests that include PCBench, 3DBench as well as time demos of DOOM and Quake.
Let’s look at the results via a bar graph, because I love graphs.
As we can see the poor Intel dx2 66mhz lags behind in all respects but surprisingly in some tests like DOOM it actually fairs pretty well against the Cyrix 100mhz. The AMD 5×86 133mhz is fairly close in terms of performance to the 83mhz Pentium Overdrive while the Cyrix 5×86 120mhz and AMD 5×86 160mhz lead the pack. Overall the AMD overclocked at 160mhz beats out all other chips including the Cyrix 120mhz in all tests except 3dBench where it only lags behind the Cyrix by about 1 FPS. Notice that the Pentium Overdrive dominates in the Quake test beating all other chips. This can easily be explained as Quake relies heavily on the FPU math coprocessor and is optimized for Pentium code. I would assume though that if I had a 133mhz Cyrix 5×86 it may beat out the AMD 160mhz in all tests being top dog.
So my conclusion on the best chip to push the socket 3 platform to its limits? Well it depends a little bit. Without considering a Cyrix 133mhz chip the top dog is obviously the AMD 5×86 overclocked to 160mhz. The other great thing about this chip is its availability, low cost and solid stability even when overclocked. It would definitely be the first chip I would recommend.
The Cyrix definitely has a sort of “cool” factor but it does involve a little more fine tuning with enabling enhancements. due to the higher price, scarcer availability and more hassle I probably wouldn’t recommend going the Cyrix route unless you want to be different or if you don’t want to overclock and can find a true Cyrix 120mhz chip on the cheap. Again I think overall a Cyrix 133mhz would beat all competition but if it was me I would be afraid to run and wear out such a rare chip.
Last up we have the Pentium Overdrive which despite its slower clock puts up a valiant fight beating the Cyrix 100mhz in all tests and running a slight edge in general over the AMD 133mhz. Again, the motherboard compatibility with the PO is not going to be as good as the AMD but if you plan to play a lot of later DOS games or Win9x games that take advantage of Pentium coding such as Quake or Duke 3D this may be the way to go. Pentium OD chips aren’t too rare but are generally more pricey than the AMD chips or the Cyrix 100mhz chips.
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