PC Overclocking for DOS games, what are the gains?

Introduction:

Hello there! Do you have a DOS rig, and would like more performance for free? You’ve come to the right place!
This article will explain my findings in DOS benchmarking and hardware tweaking, and how you can do the same!

The system used consists of the following:

• Pentium 2 ranging from 233Mhz to 350Mhz, on 250 and 350 nanometer processes.
• S3 Trio64 4MB as video card.
• Hynix PC133 CAS Latency 3. (More about that later)

Principle:

In my all-day benchmarking run which you can find here, it came to my interest that bumping memory speed as a higher priority compared to processor speed yielded it better FPS then purely processor tuning.

So going by this discovery I for one chose the fastest memory I had. This would mean that when I would bump up the FSB (Front Side Bus), that same speed will also count for the memory.

(Skip if you don not need an explanation of the way FSB and Multipliers work.)
The Front-Side-Bus is the bus between processor and memory, thus because this motherd goes up to 133Mhz FSB, and the memory does too that would mean that the memory was NOT being overclocked.
This matters because memory overclocking can result in many errors you might not even be able to see, thus hurting performance unnoticed.

So, by making sure to push the processor as far as it can go, but also getting the memory higher would get a best-case-scenario where you would push more bandwidth to the system and also pushing the processor further.
Processor speed is done with what is called a multiplier, where the real speed of the processor is as a formula: FSB times Multiplier is real speed.

For instance, if you have an FSB of 66Mhz which is most common and a multiplier of 4, that would give you a true processor speed of ~266Mhz. The first Pentium 2’s were 233Mhz. So by math, 233 devided by 66Mhz gives a multiplier of 3.5!

Practice:

So, by fine-tuning the FSB and Multiplier, we can get the memory bandwidth higher to feed the processor more data as itself will become faster as well.

Look at this table:

Now that we have the processor under control, and by the formula mentioned above the processor in this table got problems above 361Mhz. Turning it down with the multiplier now allows use to get the FSB higher, thus giving the processor more bandwidth then it had before.

Would you look the last result in the table! We are gaining performance in the benchmark, even though the processor itself is running slower! As explained, the FSB is also tied to the memory. By giving the system fast PC-133 memory we can go ham until the processor can’t keep up. Now, we have given this processor all the speed it can happily take and the memory is running nicely along!

Results:

Again, the results in here, tell the following:

The Pentium 2 266Mhz on the older 350nm process tested the fastest and more stable then pushing my 233Mhz model in the same way. (Model for this processor: 80522PX266512 SL265)

Now lets look at the beginning, completely at stock we get 25.9 frames per second, and after 83Mhz FSB on 4x and 103Mhz on 3.5x we come down to 3x. The FSB is now running at 124Mhz feeding the processor with much, much more data than before. The processor itself started to crash before at 361Mhz but runs happily at 372Mhz.

This resulting tune gives us now 40.6FPS, and in SysBench (another benchmarking tool) we get a score of 431.37.
Now, comparing the results from these two programs where SysBench is more general and PC Player represents the game;

We get a gain from 25.9 to 40.6 FPS in PC Player, thus gaining 56.76% more performance!
And from SysBench, we started with 309.69, and ended at 431.37. Thus gaining 39.29% performance!

And it doesn’t stop there, using the same tuning as before:

	Non-Tuned	After Tuning	% Gained
PC Player Benchmark:	25.9	40.6	56.76%
Quake 1.06 320×240 Timedemo	64.4	87.8	36.34%
Quake 1.06 320×480 Timedemo	25.3	32.7	29.25%
Quake 1.06 640×480 Timedemo	43.2	66	52.78%
DOOM 1.9 Min.Details	301	367	21.93%
DOOM 1.9 Max.Details	73	101	38.36%
3DBench 1.0c	195	315	61.54%
Chris’ 3D Benchmark 640×480	39.3	62.1	58.02%
SysBench 4.78	309.69	431.37	39.29%
		Average Gain:	43.81%

Here a couple games were tested, where it shows there are some very big gains to be had if you tune your system for speed! All benchmarks can be found here.

Where do I begin?

That depends, the motherboard I was using to test things was an ATC-6250. Not really a branded thing.
Multipliers where on a DIP switch block, and the FSB contols were in the BIOS under “Chipset Features”.

Thus it depends on where those two settings are located on your system, maybe on the motherboard itself, maybe in the BIOS. Who knows!

I would begin with the multipliers, turn those up bit by bit and see if you get any gains. If not, turn them back.
The possibility to do this also depends on your processor, some have this value locked, some do not. Search for yourself if your processor has an unlocked multiplier.

In both cases, if you have the multiplier locked or unlocked both will work fine for FSB based overclocking.
Turn it up bit by bit, and see if any wierdness like glitches or bugs start to appear. If they do, dial the FSB back and re-test until you have found something that works for you.

Then as the ultimate goal, for a system like this Pentium 2 it is most efficient to turn the multiplier down, and the FSB up. Reasons why were explains before. Find the sweetspot in game FPS and general processor speed, and enjoy!

Notes:

• If your system has an AGP slot andthe FSB is turned higher then 100Mhz this might cause problems. See if you can keep the AGP slot at a locked frequency or use a PCI graphics card.
• Keep the processor cool! If your system has a small cooler, be careful to not let the processor overheat or buy a better heatsink! I had this happen way back when and it did in fact kill the processor!
• Multiplier might seem like it works but the system can be slower. Check with SpeedSys or other software to check for sure that your system is indeed running at the speeds that it reports.
• 350 nanometer Pentium 2 processors have unlocked multipliers, while 250 nanometer models do not. Check before you buy!

Conclusion:

Overclocking in DOS can do a lot for the system, maybe you want to run a game like Descent, or other late-era DOS games. A little bit of tuning might help!

We hope you have fun sqeezing every little bit of potentials out of your system and see what it is really capable of, thank you for reading!