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In 1993 the Computer world was beginning a new era. The venerable 486 was ruling the roost and hard core PC gamers were enjoying 66mhz DX2’s and VLB bus video cards. A new era though was just around the corner featuring a world of improved 3d gaming and performance due to a new expansion slot type and a new CPU. This was the dawn of the Pentium.

This new generation of CPU’s named the Pentium (just a fancy name for Intels 5×86 chips brought about due to the fact Intel could not trademark a number) required a new socket type to support them. This socket was the socket 4. With the Pentium a new type of expansion bus was also starting to appear more and more. This was the PCI bus were all still familiar with today. The PCI bus was not exclusive to the Pentium and could be found on late model 486 motherboards but starting with socket 4 is when it began to be considered standard on motherboards.

Socket 4 supported only two chips. The first generation Pentium 60mhz and the 66mhz. Looking back they were a little underwhelming, expensive and always ran hot at 5 volts but they were the cutting edge in 1993 and they offered significantly better FPU (or floating point math) then the 486 chips which the new crop of 3D games would take advantage of. To compare, the original 66mhz Pentium was about equivalent to a 100mhz dx4 486 chip.

In this article I’m going to take a look at what would be a typical high end socket 4 build from about 1994, so pre-windows 95. Building a 94 period correct machine rather then a 93 one opens up many more possibilities since PCI really didn’t come into its own until 94. In 93 there weren’t a lot of PCI cards available and in all likelihood someone that splurged in 93 on a socket 4 board may of been stuck with a ISA video card for few months.



This would be a case very typical of the era. By this point the desktop form factor really seemed to be fading away as far as home computers go and a majority of new PC’s in homes were of the taller but usually less internally cramped tower design. Of course an IDE hard drive like the one I have installed was standard by now as well as the 1.44MB 3.5 inch floppy drive. A lot of machines from the era still had a legacy 5 1/4 inch 1.2mb floppy drive as well to support older software or games you were likely to still have from a previous 486 or 386. The CD-ROM drive was also starting to become standard fare now as more titles were being released in the format and popularity of the CD was bolstered from the hit game Myst that was released the year before in 1993 on CD-ROM.

The motherboard I’m using in this machine is a socket 4 Intel PM-900 with what I believe is the Mercury chipset. It still has many features that were more common with a 486 motherboard such as on board l2 cache and an AT style keyboard. It does feature three of the then cutting edge PCI expansion sockets and four older 16 bit ISA slots. To be honest I was initially surprised by the lack of features on this board. Even if it was a low end socket 4 board you would expect manufactures to want to go all out for something that at the time was an expensive state of the art board. a PS/2 mouse port or connector for a header would of been nice as well as on board IDE or floppy connection. Many of these things were even starting to show up on 486 boards of the time.

There are also some interesting peculiarities on this board such as the inclusion of a connector for a turbo led but no turbo switch. Instead of a jumper to select if your using the 60 or 66mhz CPU this board requires you to swap out the oscillator not unlike many 386 era boards. Also the board features jumpers for the PCI slots and these assigned IRQ’s. I have never noticed this on any board before.


Taking a closer look


1) CPU – The real star of the motherboard was the cutting edge Pentium processor. You had only two options with socket 4 and those were the two early P5 Pentiums that came in either 60mhz or 66mhz. Mine is the faster 66mhz. both these CPU’s ran at 5.0 volts when as all Pentiums after ran at 3.3 volts. You did have one option though for upgrade and those were the socket 4 Pentium overdrive chips. these chips would boost a P60 system to 120mhz and a 66mhz system up to 133mhz which is pretty significant. Unfortunately these overdrive chips are pretty uncommon and when found expensive. These upgrade chips also weren’t released until later in 95 or 96. The Pentium 66mhz is roughly comparable to a 100mhz dx 486 though with a superior FPU performance as I said earlier. These chips did noticeably outperform the gaming standard of the day which was the 486 66mhz DX2 but later 486’s like the 133mhz 5×86 from AMD with a Pentium rating of 75 easily beats the 66mhz Pentium in everything except Pentium optimized games or games that utilize FPU operations such as Quake. It has also been found that 83mhz Pentium overdrives used to upgrade 486 boards will also outperform a true Pentium 66mhz. to change the CPU from 60mhz to 66mhz or vise vera there is no jumper. you need to change the oscillator. The oscillator is obscured in the image above by the wires but its located above the CPU and to the right of the large chip under that bundle of wires.


2) L2 cache – the on board L2-cache, all of the Pentiums up to the Pentium II lacked on chip L2 cache so as before L2 cache was accessed from the motherboard. The PM-900 supports up to 256k of L2 cache which is pretty standard for the time and the amount I have installed.

3) RAM – this board supports up to 192MB of 72 pin DRAM via six slots. As far as I can tell it does not support EDO RAM. Its a bit of an unusual number but 192MB would of been an outrageous amount of RAM for the time. I have a more conservative 32MB’s installed which would be more common for the time on very high end pimped out builds like this one. At the time though many machines still happily ran 8mb or 16MB’s so even this is overkill.

4) AT power connector

5) AT keyboard port

6) CMOS battery – this board uses the infamous Dallas real time clock. these clocks were basically lithium batteries in a hard plastic shell. Though they don’t have the same level of leaking risk as the old barrel batteries they are sometimes pretty annoying to replace. they can be hacked to allow for cheap and common lithium battery replacements.

Now I’m going to go over some expansion cards that would be pretty common for a machine of this type. I’m not going to talk about modems cards cause they bore the hell out of me but a PC of this era would usually have some sort of ISA or maybe PCI networking card or modem.

Multi I/O – since there is no IDE or floppy controller built into this particular board I needed a I/O controller. This is the one that came with my board. Its a Winbond chip based card and nothing special but it gets the job done for floppy and IDE support as well as giving me a serial and parallel port.


Video – The choice of early PCI video cards seems to come down to two brands, ATI and S3. You also need to ask whats more important to your specific built. DOS performance or Windows (3.1) performance. Some cards are better in DOS and some Windows. The ATI mach64 supposedly was released in 94 but all the cards I found had a BIOS date of 1995. This left me with a PCI ATI Mach32 and an S3 Vision 864. after some benchmarks the 2MB Vision 864 did come out ahead in DOS but I never tested in Windows. The Vision 864 like the trio that would come later was a great card for the time offering excellent compatibility with games and other software. Other options are the venerable et4000 which should of had an early PCI version available.


Sound – There are a multitude of option for sound such as the PAS16, Adlib gold or Gravis Ultrasound that were out in 94 but all of said cards are rare and expensive. The sound Blaster 16 line on the other hand was widely available and almost all games supported it. My board came with Acer Magic S30 which is just a SB16 that used a early version of the Vibra chip. This card has a real OPL FM chip, some various CD drive headers as well as a wavetable connector for a daughter board. Its not as fancy as the other cards but its a hell of a lot cheaper and just about everything supports it. This card does suffer from the “hanging midi” bug though. I should point out on this build I actually am using the on card controller of this sound card to run my CD-ROM drive.


So, is a socket 4 machine worth it to collect now and was it worth it back then. To address the second question first, No. The Pentium 60 and 66mhz were insanely expensive when they were first introduced. Throw in the fact they ran hot and were fairly unreliable and they just weren’t smart buys, even with the power boost. Consumers were far better off waiting for a 100mhz DX4 or better yet a AMD 133mhz 5×86. Many early software wasn’t yet optimized for the Pentium or took advantage of its superior FPU abilities that only later 3D games like Quake would heavily use. Now are they worth having presently as part of a retro PC collection, maybe. The price of these CPU’s and motherboards keeps creeping up as they become more and more rare. For practical use though in an actual running retro game PC there more of a novelty and best avoided. A retro gamer is far far better off with building a socket 5 or 7 machine as those Pentiums are more powerful, cheaper, and far more reliable then the socket 4 types.


benchmarks Pentium 66mhz, 256kb l2 cache write-through, 32mb fpm RAM, s3 Vision 868 2MB

3DBENCH – 56.4 FPS


DOOM – 37.78 FPS

Quake – 14.1 FPS

same setup with a ATI Mach32 1MB

3DBENCH – 49.0 FPS


DOOM – 36.03 FPS

Quake – 13.6 FPS

Pentium 66mhz, 256kb l2 cache write-back, 32mb fpm RAM, ET6000 4mb



DOOM – 40.6 FPS

Quake – 14.8 FPS


  1. I think the early Pentiums at that speed only did better with their FPU instructions compared to the high speed 486 which I suspect actually did better on the standard integer processing. So unless you were using the FPU a fast 486 was commonly better than these slow pentiums. I believe a big part of it was the technology in the mainboards needed to catch up with the pentium. However once they hit about 100Mhz, they left all the 486’s in their dust.

    It would be interesting to try benchmarking the two processors with as similar hardware as possible.


    • yhea, my AMD 5×86 machine at 133mhz beats the Pentium 66mhz in every benchmark EXCEPT Quake which makes sense since Quake was Pentium optimized and took advantage of the FPU. not many games prior to 1997 used the FPU much unless it was CAD. Falcon 3.0 and Sim City come to mind but not many others. the Pentium 66mhz is roughly equal to a Intel DX4 100mhz 486 as far as integer processing but it blows everything else out of the water FPU wise. My Cyrix 5×86 120mhz comes close but that chip is really less 486 and more next gen as opposed to the AMD 5×86 which is just a supped up 486.

  2. Your Doom score seems a bit low – did you run the test full screen?
    If you’re interested in comparisons regarding Doom shareware demo3 you may find Anton’s

    interesting. LOTS of scores and really cool to see how big a delta, between a cpu’s score in a great vs. a bad “working environment” aka chipset + (cache/main)mem + gfx card, can be established.
    BUT, all scores are gathered with the screen size decremented twice -> HUD + 1 vertical/horizontal border.

    The Pentium6x needs a good chip set to shine and there seems to be only one high quality option, the SiS501/502/503 which gives the CPU a little more room to breath.
    Former runs in ECS’ “SI5PI/AIO” which has a pompous 16 + 2 cache configuration thus enabling running the fastest timings if fully equipped. This is topped off by a hefty 1MB 2nd level max. cache size. M Tech.’s “R512” even allows 2MB of 2nd level(16 times 128k x 8 srams) but I have never seen one in real life.

    You could try to change the oscillator which drives the cpu/fsb.
    I have done so on the Siemens/D841(inserted a DIL8 socket) and I can now run the system up to 75mhz with active cooling(Northbridge needs a 486 cooler though) and the CPU has a chunky socket 7 cooler attached… preventing 0.8µ meltdown. Both heatsinks are of course “well lubed” with MX4 paste.
    Its’ very interesting that both the cpu/chipset(LX) are able to withstand this speed – it also finished MemTest2.11 and the usual Quake/Doom/Blood torture tests. The mod turns the system into a really interesting oddity.

    The worst chipsets seem to be of the Opti variant, which seemed botched both bus- and otherwise.

    Take care

    • Thanks for the comment and info. Yes, I did run the bench at fullscreen. Unfortunately socket 4 boards seem to be harder and harder to fine. Id actually really like to try out some of your suggestions if I wasnt to afraid of killing the board. I already had a capacitor randomly die in spectacular spark and smoke fashion. Thankfully the board was fixable and still runs fine. Maybe one day though I’ll try out this overclock.

  3. Could you re-run Doom timedemo demo3 resized(2 times MINUS_KEY after fullscreen)? Cachchk7 and speedsys scores would also be appreciated. You could try running a Matrox

    You can’t kill the board by changing the oscillator, albeit since yours is already equipped with the 66mhz variant you could just ignore higher clocks and play it super-safe via attaching heatsinks to all chipset chips and put a bigger one onto the cpu(tall socket 7 coolers are very adequate at keeping the chip temperature down BUT you have to be inventive with the attachment).

    The obvious strategic idea behind the oscillator “upgrade” is to make up for a slightly lagging chipset by clocking it higher… the CPU is of course driven beyond “levels of compassion” which may cause a sweaty forehead on the preservation focused retro owner.

    If you’re on the hunt for a SI5PI-AIO board I know one possible source but it may cost you a hefty 200$ excluding shipment – the board’s in excellent condition of course.

    Happy New Year,

    • sorry for the late reply. I’ve been pretty busy lastly but I do have the P66 on hand so I’ll try and run the benches as soon as I can. For the DOOM timedemo Ive just been using Phils benchmark suite that runs the demo automatically. how do you go about running the demo and adding the parameters you suggested?

        • Viktor
        • Posted January 7, 2018 at 10:20
        • Permalink

        Run Doom with….
        ‘doom -nosound -nomouse -timedemo demo3’
        BUT before you do aforementioned, start it and adjust the screensize. If you’re unsure then just alter ‘default.cfg’ – the line in question should read ‘screenblocks 9’ as 11 means fullscreen. It’s just a measure to make the results comparable with the “semi-official” ‘Doom benchmark results’.
        One more thing – how is this machine’s BIOS… lots of tweaking or minimalistic?

        p.s.: I’ll snatch the board myself then.

    • So, I pulled out the socket 4 beast and realized I changed video cards to a ET6000 a good while ago and had no idea where the others were buried so I had to do the test with this card installed. I have updated my benchmarks in the article.

      The BIOS on this motherboard is extremely spartan. doesn’t give many tweaking options at all. just to add wait states to DRAM, set DRAM refresh to “hidden” or “normal” and to enable/disable cache. all my cache were enabled but I did notice it was set to Write-Through so I set it to Write-Back and noticed a small (less then 1 FPS) performance bump in the benchmarks.

      here are the results of the tests you suggested with the ET6000 and write-back enabled

      speedsys – 50.42 speedsys mem tests L1 -120.02 mb/s, L2 – 56.33 mb/s mem throughout 35.41 mb/s

      cachechk – L1 – 91.4, L2 – 65.1, main mem – 49.8, RAM access – read – 168ns, write 307ns

      DOOM bench ran as you instructed gave a result of 44.3 FPS

  4. Thanks a billion!

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