That looks like a solid rig for DOS gaming. Especially love the choice of sound cards. 😉

DOS tends to max out at 64MB of RAM, so 256MB is overkill but there's no inherent downside. And DOS games typically won't use more than 8MB to 16MB, with rare exceptions.

Pentium 233MMX and S3 video card should be able to run Duke 3D at 640x480. Blood and Shadow Warrior are a bit more demanding, but should be playable. If you want better 2D performance, a Riva 128, Matrox Millennium, or Matrox Mystique could offer higher frame rates at the cost of reduced compatibility with some games. Personally, my favorite card for a build like this would be a Riva 128.

A faster CPU can help push higher frame rates for DOS games that can take advantage of it (generally 3D games that use software rendering). And if you wanted to do a multi-boot with Win 95 or 98, it could give you more performance under those operating systems.

The only other thing I would add to the build would be a Voodoo 1 graphics card to take advantage of some of the early Glide-supported DOS games. But that depends on which games you want to play, of course.

Cool build, seems well balanced.

If you are in USA you can get a K6-2+ 400 for $19, I just got one from this specific seller and it looks like a brand new CPU, I was also able to mod it to a K6-3+ enabling the additional 128kb of L2 cache.

mrzmaster wrote on 2025-02-03, 17:27:

Diamond Speedstar A55 AGP 8MB (S3 Trio 3D/2X)

The S3 Trio3D/2X AGP has one of the fastest 2D performance, very good DOS compatibility and comes VBE 2.0 onboard with a truckload of VESA video modes. I highly recommend S3VBEFIX utility for that card.

The only downside is performance regression with Build-based games (related to VBE's protected mode interface) that wasn't present on previous S3 cards but thankfully, I have a workaround that involves UniVBE.

If one can be sourced cheaply, is there any value to getting a faster CPU such as an AMD K6-2+ for DOS usage?

Yes, a K6-2+ allows you change the CPU multiplier on the fly thru utilities, from 2.0x to 6.0x (except 2.5x). Another advantage is write-combing support, used to improve framebuffer performance.

Would there be any downsides to this?

Non-pipelined FPU, but that's mostly irrelevant for DOS games.

Hang on... that's a rev 1.05 P5A(-B). The rev 1.05 and later boards have a hardware bug that mean they don't work properly with K6Plus CPUs. If you want to run one of them, you need to do a little mod.

Don't want to mod? Stick to K6 2/3 non-plus on these revisions.

Shponglefan wrote on 2025-02-03, 17:42:

If you want better 2D performance, a Riva 128, Matrox Millennium, or Matrox Mystique could offer higher frame rates at the cost of reduced compatibility with some games. Personally, my favorite card for a build like this would be a Riva 128.

What compatibility issues might I run into with a Riva 128? I also noticed that Riva TNT's seem to be plentiful and cheap - would this GPU be in line with a 128, in terms of compatibility?

Gmlb256 wrote on 2025-02-03, 19:24:

The S3 Trio3D/2X AGP has one of the fastest 2D performance, very good DOS compatibility and comes VBE 2.0 onboard with a truckload of VESA video modes. I highly recommend S3VBEFIX utility for that card.

The only downside is performance regression with Build-based games (related to VBE's protected mode interface) that wasn't present on previous S3 cards but thankfully, I have a workaround that involves UniVBE.

Thank you! I will definitely check this out!

dionb wrote on 2025-02-03, 20:57:

Hang on... that's a rev 1.05 P5A(-B). The rev 1.05 and later boards have a hardware bug that mean they don't work properly with K6Plus CPUs. If you want to run one of them, you need to do a little mod.

Don't want to mod? Stick to K6 2/3 non-plus on these revisions.

I looked at the mod and this might be beyond my current capabilities. What is the difference between the regular K6 2/3 and + variants? Moreover, what's the difference between the K6 2 and 3? Just the L2 cache on the K6 3?

mrzmaster wrote on 2025-02-05, 17:05:

What compatibility issues might I run into with a Riva 128? I also noticed that Riva TNT's seem to be plentiful and cheap - would this GPU be in line with a 128, in terms of compatibility?

Riva 128 is great for DOS compatibility in my experience. I was thinking more of the Matrox cards when I wrote that out. I should have been clearer in that.

Riva TNT should be similar of DOS compatibility. nVidia cards in general tend to be solid DOS performers in my experience (having primarily tested Riva 128 through GeForce FX).

mrzmaster wrote on 2025-02-03, 17:27:

256MB PC100 SDRAM (surely overkill, but I have a bunch of spare sticks)

Not just an overkill but it is very likely you'll exceed the cacheable area of your motherboard.
512 kB Cache -> 64 MB write back & 128 MB write through
1 MB Cache -> 128 MB write back & 256 MB write through

Disruptor wrote on 2025-02-05, 18:27:

Not just an overkill but it is very likely you'll exceed the cacheable area of your motherboard. 512 kB Cache -> 64 MB write bac […]
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mrzmaster wrote on 2025-02-03, 17:27:

256MB PC100 SDRAM (surely overkill, but I have a bunch of spare sticks)

Not just an overkill but it is very likely you'll exceed the cacheable area of your motherboard.
512 kB Cache -> 64 MB write back & 128 MB write through
1 MB Cache -> 128 MB write back & 256 MB write through

This is another thing to keep in mind when it comes to what CPU you use as the chipset's cacheable area becomes a moot point if you use a K6-2+, 3+ or a standard K6-3 with their on die L2 cache.

Shponglefan wrote on 2025-02-03, 17:42:

Pentium 233MMX and S3 video card should be able to run Duke 3D at 640x480. Blood and Shadow Warrior are a bit more demanding, but should be playable. If you want better 2D performance, a Riva 128, Matrox Millennium, or Matrox Mystique could offer higher frame rates at the cost of reduced compatibility with some games. Personally, my favorite card for a build like this would be a Riva 128.

I just wanted to add to this...

I have an S3Virge/DX PCI 4MB paired with a slower IBM (Cyrix) 6x86L-PR166+ running at 133MHz in my dedicated DOS 6.22 system.

DN3D does indeed run good at 640x480. Blood also runs good at 640x480 with the detail slider at max. Even Fallout and Descent both run great on this setup. I don't have Shadow Warrior installed on there to test.

I went with the S3 card I did for wide ranging DOS support, and have been surprised how well it works in the 3D games I've tried. Quake is the most demanding game I have on that build, and it does indeed run at 640x480, but it's noticeably slow, however it runs perfectly at 320x240 so that's where I leave it.

Disruptor wrote on 2025-02-05, 18:27:

Not just an overkill but it is very likely you'll exceed the cacheable area of your motherboard.
512 kB Cache -> 64 MB write back & 128 MB write through
1 MB Cache -> 128 MB write back & 256 MB write through

Does that mean it will actually be a detriment to performance to use 256MB? What would be the optimal RAM amount to use?

Repo Man11 wrote on 2025-02-05, 18:36:

This is another thing to keep in mind when it comes to what CPU you use as the chipset's cacheable area becomes a moot point if you use a K6-2+, 3+ or a standard K6-3 with their on die L2 cache.

Due to the P5A-B v1.05 hardware bug, I don't think I'll be using a K6-2+/3+ and standard K6-3's seem to be rare/expensive. Standard K6-2's seem to be cheap and available, so I will probably go with one of them. Similar to my question above about RAM usage, what is most optimal to use with this CPU?

StriderTR wrote on 2025-02-05, 19:39:

I have an S3Virge/DX PCI 4MB paired with a slower IBM (Cyrix) 6x86L-PR166+ running at 133MHz in my dedicated DOS 6.22 system.

DN3D does indeed run good at 640x480. Blood also runs good at 640x480 with the detail slider at max. Even Fallout and Descent both run great on this setup. I don't have Shadow Warrior installed on there to test.

Thanks for the feedback! I will give the S3 Trio 3D a fair shot before I think about replacing it with a Riva card.

I hadn't checked prices for a while; the last time I looked there were K6-3 400 MHz CPUs for a pretty reasonable price on Ebay, but I'm not seeing them now. Then again, inflation has been raging the past few years so it's hard for me to really estimate what things are now worth because my money doesn't have the buying power it once did. If you go with a standard K6-2, my preference would be the fastest one at a reasonable price. I would definitely benchmark the system with both the maximum cached RAM versus the amount you would prefer to install and see if there is a significant performance hit.

mrzmaster wrote on 2025-02-05, 17:05:

[...]

I looked at the mod and this might be beyond my current capabilities. What is the difference between the regular K6 2/3 and + variants? Moreover, what's the difference between the K6 2 and 3? Just the L2 cache on the K6 3?

K6-2: basic model, no on-die cache. 2.2V. Runs up to 570MHz (officially) with a bit of OC headroom.
K6-3: K6-2 with 256kB on-die cache. 2.4V (depending on core revision). Runs hot, 450MHz is official max, almost no OC headroom.
K6-3+: die-shrink, mobile CPU with more power/clock options, also 256kB on-die cache. 2.0V. Runs cool, officially only released up to 500MHz, but reliably runs at 600MHz, and sometimes can go even higher.
K6-2+: K6-3+ with half the cache disabled (either due to errors, or just binning)

The + CPUs need specific BIOS support - and use a pin the non-plus doesn't, specifically the pin that's incorrectly connected on your motherboard revision, hence the mod.

Clock-for-clock there's no difference between K6-3 and K6-3+, the + just clocks faster (and can be clocked slower too). K6-2+ is slightly slower, but difference is minimal. All three are a lot faster than K6-2 without that on-die cache. Most likely a K6-3 450 would be the fastest CPU to run correctly on your motherboard without the mod. A K6-2 550 would only outperform it in corner cases where cache is almost irrelevant.

mrzmaster wrote on 2025-02-05, 20:37:

Disruptor wrote on 2025-02-05, 18:27:

Not just an overkill but it is very likely you'll exceed the cacheable area of your motherboard.
512 kB Cache -> 64 MB write back & 128 MB write through
1 MB Cache -> 128 MB write back & 256 MB write through

Does that mean it will actually be a detriment to performance to use 256MB? What would be the optimal RAM amount to use?

64 MB.
Depends on the operating system. DOS won't have any problems as it is likely that never will use the area above 64 MB.

mrzmaster wrote on 2025-02-05, 20:37:

[...]

Does that mean it will actually be a detriment to performance to use 256MB? What would be the optimal RAM amount to use?

Depends on how much you use.

WB Cache is slightly faster than WT cache is faster than RAM is *MUCH* faster than thrashing to HDD.

So if you use less than the WB limit, it's fastest to stay within that limit with your RAM. If not, switch to WT if you can stick within that limit. Finally, if you use more than the WT limit, it's always faster to have uncached RAM than thrashing to HDD (swapfile).

You say you want to play DOS games. There are basically no DOS games that use more than 16MB, so there is no benefit to go over that in a pure DOS system. In fact, it just adds irritations (a lot of memory detection routines in DOS games can't handle large amounts of RAM - I hit this last week, games that refuse to run if you have 64MB because they detect <2MB of RAM)

Win3.11 bumps that up a bit, 16MB is useful there (far better than 8MB, I clearly remember that upgrade in 1996 😉 ), but you don't need a whole lot more.

Win95 runs best between 24 and 32MB, so again no need to even approach the lower caching limits.

With Windows 98SE things get interesting, 64MB will work but 128MB will run better. The added value of going over 128MB on an So7 system is limited. This is a use-case for setting L2 to WT and installing 128MB.

As for Win2k/XP (and Unixen), they can run on less, but basically they take as much RAM as is available. Also, they are smart enough not to run everything in the uncached areas. Here, just max out your RAM regardless.

Note: all this applies to the L2 cache on the motherboard, not to any cache on the CPU. So all compatible CPUs have L1 cache and the K6-3 and K6plus CPUs can also cache everything in their on-die L2 cache. The motherboard cache becomes L3 and while it doesn't hurt performance, it's nearly irrelevant in the big picture. So with one of those CPUs you can safely max out RAM without performance hit.