ancientelectronics

continuing with the Anatomy of series we will be looking at a Windows 3.1 computer designed to push the 486 CPU to its limits. Windows 3.1 or Windows 3.11 for networks was an earlier windows operating system that basically added a graphics user interface to DOS. you had to already have DOS installed and for the most part it made DOS more user friendly and allowed the user to run something sort of like what we know as Windows today. You could easily exit it to DOS and vise versa. There were also a number of games designed to run within Windows 3.1 exclusively or with a different “enhanced” interface.  For the most part Windows 3.1 installed on a PC did not interfere with DOS applications or games, In another instance of “I swear I’ve read it somewhere” I seem to recall a few games that had issues running if windows was installed or some hardware issues arising since windows does some modifying to the config. files and other such important files. Again, I cant confirm this but I swear I’ve read about these issues somewhere before. for compatibility sake though and as a simple excuse to have another PC setup I do run a windows 3.1 exclusive PC and keep “pure” DOS computers as well.

Is the creation of a PC purely for Windows 3.1 really necessary? No, not in the slightest, it’s a rather small era in PC gaming and from what I can tell the incompatibility issues with Windows 3.1 are so negligible your actually probably better off having it on a DOS PC if you only have room to spare for one PC. That being said since I do this as a hobby and have room for PC’s of every minute era or purpose I like to treat this as sort of experimental setup. although Windows 3.1 could run on older hardware like the 386 It was really meant for the 486 CPU and I want to take this setup as a PC that pushes the 486 platform to its limits. Practically speaking if you’re looking at a very fast 486 you may as well get an early Pentium as its faster and cheaper but if you want to see how far the 486 can be pushed then a Windows 486 machine is a fun project.

A nice little tower representative of the era. nauseating off-white and the standard CD-ROM, 5 1/4 and 3 1/2 floppy drives as all three of these formats were still in fairly wide use at the time. For a hard drive we have a 500MB IDE hard drive loaded with DOS 6.22 and Windows 3.1, of course a larger hard drive can be installed but again without partitioning or some tricks about 500MB is the most DOS can “see”. This tower also comes with one of those neat little LED screens that displays the current CPU speed of the computer, handy on an older computer if you have a turbo button hooked up so you can visually see the CPU speed setting. Yes, its running at 133mhz, no it’s not overclocked and no, it is not a Pentium, we will get to that in a moment.

you can always add a PCI SCSI card as well. SCSI is usually a little faster then IDE and allows larger hard drive sizes but back in the 80’s and 90’s it was more expensive then IDE. SCSI cards also generally have a external port on them for hooking up several external SCSI devices. The Maxtor hard drive I have in this machine is actually pretty fast and since I already had a lot of information on it and I do not use this PC to much I decided not to switch it over to SCSI (yet) but if your just building a similar system I do recommend a ISA,VLB or preferably PCI SCSI controller card. Another reason I haven’t bothered with SCSI though has to do with bus mastering issues with certain machines. specifically ones that use the AMD 5×86 and write back RAM like this one. apparently you can only have one of the other so with this machine I’ll stick with IDE.

A pretty standard rear view of the unit with the typical serial connections and expansion cards installed. This PC like most of the era uses the large AT keyboard port and a serial mouse. please refer to my previous Anatomy of posts for more information on these older keyboard/mouse connection standards.

MOTHERBOARD – Next is the all important motherboard or MB. To push the 486 I went with a very late model MB that incorporated PCI slots. generally I don’t recommend PCI 486 motherboards because first of all they are slightly hard to find and expensive as well as the PCI slots in them are sometimes a little buggy due to the fact this was a new expansion slot format at the time but since this is more of a project machine we will incorporate the PCI slots to give us access to some faster PCI video cards. You will also notice another of those slot fans I love to throw into my cases, again, its somewhat unnecessary for this setup but you really can never have too much cooling in a PC.

The motherboard I am using is the infamous PC Chips M919 motherboard

This board has a pretty bad reputation but as far as 486 boards with PCI slots it seems to be the most common and as far as I’ve seen stable enough for normal usage. It has three PCI, three ISA and one VLB expansion slots making this a very versatile board. Also this board is DX4 compatible to support the last line of the 486 CPU’s the DX4. so what makes this board so infamous. The answer for that will usually be the legal dubiousness of these.

See, back in the day cache chips which is a much faster secondary RAM on the motherboard the CPU can take advantage of was really expensive. Reputable motherboard manufacturers if they were making low cost boards would simply not include them on the board but on the most M919 boards there are “decorative” cache chips. That is to say completely fake chips there to fool you into thinking your board actually has L2 cache. Even on board the screen proclaims “Write back cache” but alas.

Without L2 cache your performance loss is probably somewhere under 10% depending on the CPU your running. Its not horrible but not great either. Fortuitously these boards do have a COAST-like slot that a special 256kb Cache chips can be installed into. Do not confuse this module with the more common ones that are meant for some Pentium boards. Installing the wrong module could damage the board.

Here is the official and uncommon cache module. Notice the back side specifically states for use with M919 board. Once installed the boot up BIOS screen should change to “256kb cache” but run a cache checking program like cachechk just to be sure.

Now this motherboard can be notoriously picky and even though my board detected the 256kb of L2 cache at first it wasn’t actually using it and running benchmarks or cachechk utility resulted in no L2 cache detected. I wasn’t until later I discovered I needed to replace the EDO RAM with FPM for my machine to use the L2 cache stick (the performance boost from L2 cache over EDO RAM is significant so choose L2 cache if you have to chose only one). Maybe a different brand of EDO RAM would fix this but I did not have any other makes on hand to test. I also had to try several sticks or FPM RAM before I found sticks it would even boot with, its a very picky board. Also note that I have read that some boards may not detect the L2 cache if your using more then 32MB of RAM. Mine doesn’t seem to have this issue but yours may.

1) CPU – OK, now to the CPU. Were going to go with the fastest 486 CPU’s available and basically we have three choices. The AMD 133mhz 5X86 which is basically a supped up 486. A Intel Pentium Overdrive 83mhz which is a scaled down Pentium made to work on a 486 board and give “kind of” Pentium performance and lastly the Cyrix 5×86 which comes in 100 or 120mhz which is a scaled down version of Cyrix’s next gen 6×86 chip. First I’ll briefly explain something about CPU’s. As a general rule but not always the final model or speed of a CPU generation is faster than the first of the new generation. ok, as an example the 133mhz 486 is faster than the first Pentium chips, so a 133mhz 486 is faster than a 60mhz Pentium 1, actually its about as fast as a 75mhz Pentium 1 which is pretty impressive BUT a 133mhz Pentium 1 is WAY faster than a 133mhz 486 CPU. This is usually due to increased efficiency, features and designs with the newest generation. Other examples would be the last of the Pent III’s being faster than the first Pent 4’s and the 186 CPU being faster than the early 286 CPU. so with all that being said the 133mhz 486 is a pretty fast chip for its class.

There are two types of AMD 5×86’s that I’m aware of. The straight chip from AMD that is designed to run on later 486 boards whose BIOS support DX4 chips and then the 5×86 upgrade chips.

First off is the turbo chip and I have a Kingston 133mhz turbochip which is the AMD 133DX4 sold under a different brand name with an attached fan.

This chip was designed to give individuals an upgrade path for their older 486 boards. In a dx4 compatible MB this chip should run at 133mhz. it has onboard cache and is socket 2 and 3 compatible. It’s a very fast chip and great if you do not have a dx4 486 motherboard. This issue is there a bit uncommon and can be pretty expensive. as of the writing of this article a 133mhz AMD could be had for $24 shipped on eBay where the only turbochip I managed to find was over $60. Also the turbochip is not 100% compatible with all motherboards and on some may give reduced speeds. I had mine installed in an older 486 socket 3 board and was only able to achieve 100mhz (still fast for a 486).

If your board supports DX4 chips go for a real AMD DX4 133mhz as some of the upgrade chips that are really meant for older boards have some drawbacks. For instance the above Kingston turbochip only supports Write-Though memory where as the true AMD 5×86 supports Write-Through and Write-Back with Write-Back giving better overall system performance.

Next is the 83mhz Pentium Overdrive. This is not a true Pentium and performance for regular tasks it scores slightly behind the AMD 133mhz but in 3D and tasks using the FPU or floating point math the POD does much better then the AMD.

Lastly is the Cyrix 5×86 chips which come in the more common 100mhz uncommon 120mhz and rare 133mhz. The 100mhz gives inferior performance to both the AMD and Intel Overdrive but the 120 and 133mhz chips give superior performance to both. This performance may vary though depending on motherboards and supported 5×86 features.

The AMD 133mhz is in my opinion the way to go when coupled with a DX4 motherboard due to relative availability and performance. It is a mature 486 chip that gives excellent performance equivalent to and in some cases exceeding a 75mhz Pentium 1 as well as giving rock solid reliability due to the process of 486 manufacturing being fully mature at this point. Be sure to install the CPU with a 486 heatsink and fan to keep heat levels down. Having said that I do plan on eventually tracking down a Cyrix 120mhz for my machine since the M919 motherboard I use apparently supports a few features of the Cyrix 5×86 in BIOS and I should get superior performance with it.

*update* I recently replaced my AMD 5×86 with a Cyrix 120mhz 5×86. remember to enable LSSR and LB in the BIOS if using the Cyrix chip for extra performance. the M919 is the only known board that you can enable some Cyrix features without using a third party utility. I would also advise to set your cache to 2-1-2 and your memory read/write to 0/0 in the BIOS instead of auto detect. I was told this advise by a VOGONS forum member and it really helped boost performance.

Another interesting “quirk” about this motherboard is that the PCI bus usually runs at 33mhz but when your CPU demands a 40mhz bus like the Cyrix 120 (3×40=120mhz) the PCI bus gets cut to 27mhz thus slowing your graphics card down. this has caused some games and benches to be slower with the Cyrix installed. a rare 133mhz Cyrix 5×86 or an overclocked chip running on a 33mhz bus would solve this issue. Thankfully though there is another solution. If you have a turbo button on your case as mine does you can jumper the turbo switch to JP3a. With my machine now when I boot my machine boots in 33mhz mode and the Cyrix runs at 100mhz (33mhz fsb x3). After my PC is done posting and gets to the C:\ prompt I hit my turbo button unjumpering JP3A and returning the CPU to a 40mhz bus and 120mhz speed. The PCI bus though I believe ends up being overclocked to 40mhz which may cause issues with some cards. So far my Ark card has handled it just fine.

Benchmark results

AMD 5×86 @ 133mhz, 256kb l2 cache module

3Dbench = 75.2
PCPbench = 19.7
Doom = 42.58
Quake = 12.6

Cyrix 5×86 @ 120mhz, 256kb l2 cache, video card at 33mhz (as with AMD due to jumpering trick), loop_en=off, rstk_en=on, lsser=off, fp_fast=on, btb_en=on via Peter Moss 5×86 utility

3Dbench = 95.0
PCPbench = 22.3
Doom = 48.63
Quake = 15.0

The Cyrix is now clearly beating the AMD 5×86 with the video card running at full speed and certain Cyrix enhancements enabled via a third party utility.

2) RAM – Not much to say about RAM except to pack in as much as you can. The later 486 motherboards  should pretty much all support at least 64MB of RAM. Mine is loaded to the MAX of 64MB but as I’ve said before most DOS games will run fine with about 8MB. As a fast 486 though were probably going to be playing some rather later FPS games like DOOM and Duke 3d so more RAM is defiantly better. Take note of the Ram type your Motherboard needs. its most likely going to be 30 pin or maybe 72 pin. Your also going to want a board like mine here that supports EDO RAM for that little extra speed.

3) VIDEO CARD – Now I’m going to let you in on one of the best kept secrets of DOS gaming, the ARK Logic 2000MT chipset. upon first discovering this card in my collection I looked it up as I’ve never heard of it before. At the time the only information I could find was a German wiki page that even after translation yielded little useful information. I simply tossed it aside and assumed it was a low budget no name card. It wasn’t until a few months later I discovered an online post about someone who was testing video card speeds in DOS and was shocked to find that the unassuming ARK LOGIC 2000MT was beating out all the competition under DOS and was practically neck and neck with the much praised ET4000 video chipset. After further research and reading I discovered that the ARK LOGIC cards were well praised in their time and are indeed very fast and very compatible PCI video cards for DOS rivaling the well known ET4000 family. Across the board the Trio64V2 that I use in my Pentium DOS machine from all accounts does give somewhat better game compatibility the ARK card is definatly the faster card. The ARK 2000MT chipset was also used in the Diamond Stealth64 Graphics2001 PCI card but the one I’m using is an ARK PCI card with 2MB of RAM.

4) SOUND CARD – usually the trickiest part to set up in DOS. I’m using an ISA Sound Blaster AWE32 with 8MB of added ram. Actually the card I’m using is a Sound Blaster 32 with 8MB of RAM making it almost just like a regular AWE32 except the SB32 uses the VIBRA chip which is a little less noisy then the standard chip used in the AWE32, also you cant make fine adjustments to the SB32 that you can with the AWE32 like to the treble and bass but the cheaper price and clearer sound from the SB32 makes it a good trade off in my opinion. these cards are HUGE and can be a little pricy sometimes. the cheapest and more overall compatible solution would be a Sound Blaster 16 card but I like the AWE32/SB32 for its enhanced 16 bit sound ability and good game compatibility. there are a few games (like Cyclones) that do not support the AWE32/SB32 but i find most games from the late DOS era do and many from earlier as its SB16 compatible. games like Duke Nukem 3d sound much better with this card then on a SB16 and late era games is what were shooting for with this setup. The model I’m using here is CT3930, this model has an actual Yamaha FM chip on it allowing older games that use FM to sound correct. Some models do not have an actual FM chip onboard so always look for the Yamaha chip when buying a SB32 or AWE32.

 Overall this is a very capable PC for gaming and Windows 3.1 multi tasking. As I said at the beginning there really is no pressing practical need for a Windows 3.1 exclusive PC and for a PC this fast you could do it more easily and more cheaply with an early Pentium 1 setup but for what it is it does show off the high end of the 486 platform very nicely and will play later more demanding games silky smoothly. Doom plays perfect and really only a blast from the BFG in the most monster crowded of room will even have a chance to start some small slowdown for a few seconds. Overall a fun project and a capable machine.