Search for K6-300 on google. That will give you a link to the K6 300 on CPU World.

K6-2 CPUs and possibly K6-III and maybe the II+ and III+ would work on that board. The newer CPUs support a 6x multiplier using the 2x multiplier setting on the motherboard.

K6-2 added 3DNow instructions and the K6-III and III+ and III+ have on-die L2 cache.

Is there a 75 or 83Mhz fsb setting on that board?

I hope I'm understanding you correctly. The PR just means "Pentium Rating" or "Performance Rating". This form of branding was eventually dropped because it was confusing customers.

https://en.wikipedia.org/wiki/Performance_Rating

The K6-PR 300 is the same as a K6-300 to the best of my knowledge, someone correct me if I'm wrong. They're both running at 300MHz. Older "PR" ratings had the CPU running at lower speeds, but compared them to higher clocked Pentiums. Like the Cyrix PR166+ in my TX97-XE based DOS rig, but it only runs at 133MHz. It was all really just branding.

The K6-2 300 is an updated "version" of the K6 300, and added 3DNow like Cyclone said, and will be ever so slightly faster, but I don't think it's going to be noticeable outside of a few benchmarks.

I often use this site to identify processors as well: https://cpushack.com/K6xID.html

If you need more info on your board, you can get it here: https://theretroweb.com/motherboards/s/asus-tx97-e

Hope that helps. 😀

WOW Thanks everyone!!
I get the PR now. Thanks
I have the manual. on page 17 & 18, it talks about jumper settings for CPU. I do not understand all that info and abbreviations fully. (probably just enough to burn up the board or cpu with a misplaced jumper)
The top part dose not have a K6-300 setting but the second section does.
So what would to proper jumper settings be for a K6 300?
I will flash the board to the latest BIOS, which can handle K6 300. But will it handle a K6-2 300 or K6-3 300? If so, would the jumper settings still be the same?
The board may be able to run a K2 or K3, but will the BIOS see it as that and be able to run it properly?
Again thanks for any input.

K6 PR2-xxx is an early K6 (Revision B). Never heard of a K6 PR that's not PR2, unless part of the writing has come off. And the PR2 I've not seen above 200 MHz, so it is quite uncommon at 300. I never had a full set, but the K6 family were one of the first that I collected 😀

KLund1 wrote on 2025-03-02, 08:04:

WOW Thanks everyone!! I get the PR now. Thanks I have the manual. on page 17 & 18, it talks about jumper settings for CPU. I do […]
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WOW Thanks everyone!!
I get the PR now. Thanks
I have the manual. on page 17 & 18, it talks about jumper settings for CPU. I do not understand all that info and abbreviations fully. (probably just enough to burn up the board or cpu with a misplaced jumper)
The top part dose not have a K6-300 setting but the second section does.
So what would to proper jumper settings be for a K6 300?
I will flash the board to the latest BIOS, which can handle K6 300. But will it handle a K6-2 300 or K6-3 300? If so, would the jumper settings still be the same?
The board may be able to run a K2 or K3, but will the BIOS see it as that and be able to run it properly?
Again thanks for any input.

Hi Klund1,

I will try to answer your many question. 😉

CPU Support
Official CPU support for the TX97-E has been extended up to the K6-2/400 and K6-III/400 CPUs. This was documented in the FAQ section on the German Asus Support website. An archived copy from September 2000 can be viewed here:
https://web.archive.org/web/20001207093900/ht … p5cpu_supp3.htm
The latest 0112e-1 BIOS version for the TX97-E fully supports these 400MHz CPUs.

Note that the K6-PR300 (or K6-300) was the fastest K6-1 model, so opting for a K6-2 or K6-III allows you to select a faster CPU for this board.
But unofficially, even faster K6 models are supported by the TX97-E. These are: K6-2/450, K6-2/500, K6-III/450, K6-2+/450, K6-2+/500, K6-III+/450, and K6-III+/500.
However you need the patched 0112e_J2 BIOS to get support for these faster models and speeds. You can download this patched BIOS from TRW, or from my “Unofficial K6-2+/K6-III+ webpage”. The link is in my signature below.
As an added bonus, the patched BIOS fixes the 32GB IDE HDD limit bug for full 128GiB IDE drive support.

CPU speed setting
The jumpers settings from the manual for the correct CPU speed can be confusing.

The Frequency Selection for the External CPU clock via the three FS jumpers is straightforward. This setting controls the clock frequency of the signal lines (the Bus) between the CPU, the chipset, and the memory modules. The CPU also uses this clock signal internally, and multiplies this by the Bus Frequency ratio selection to generate the internal clock speed.

The Bus Frequency ratio (or multiplier) setting via the three BF jumpers needs some explaining.
The BF jumpers do not control the multiplier directly, but just set a high or low signal on the associated BF pin of the CPU. It is then up to the CPU how to interpret this, so it is the CPU itself that selects the multiplier from the BF setting. This is not the same for every CPU model, hence the table with CPU A, B, etc. below the BF settings.
For all AMD K6 models, use CPU E.

Extra CPU to BUS Frequency Ratio settings for K6-PR266, K6-PR300, and K6-2(+)/III(+):
5.0x -> BF0: 1-2, BF1: 2-3, BF2: 2-3
5.5x -> BF0: 1-2, BF1: 1-2, BF2: 2-3
6.0x -> BF0: 2-3, BF1: 1-2, BF2: 1-2
Note that the 6.0x setting only works on the K6-2CXT, K6-III, K6-2+, and
K6-III+ CPU. Other CPUs will do 2.0x with this setting. All K6-2/400 and
faster K6 CPUs have the CXT core.

CPU Vcore Voltage
For all K6 models, the required Vcore voltage is printed on the CPU.
This are the additional Vcore settings of the TX97-E:
2.1V -> VID0: 1-2, VID1: open, VID2: open
2.2V -> VID0: open, VID1: 1-2, VID2: open
2.3V -> VID0: 1-2, VID1: 1-2, VID2: open
2.4V -> VID0: open, VID1: open, VID2: 1-2
For 2.0V K6+ CPUs, you can safely use the 2.1V setting.
For all K6-2 CPUs, use the 2.2V setting (except the 2.4V K6-2/450AHX).

CPU speeds above 400MHz
This board uses the i430TX chipset, which is rated for a maximum 66MHz clock. So the 75MHz and 83MHz settings are overclocking the chipset. But to reach 450MHz ( 6 x 75) or 500MHz (6 x 83) CPU speed, these higher Bus clocks are needed because x6.0 is the highest multiplier of the socket 7 platform. Luckily the i430TX is very tolerant for overclocking.
However, the PCI bus is connected to the chipset via a fixed 2/1 divider and normally runs at 33MHz. So with a Bus clock of 75 or 83 MHz, the PCI bus is also overclocked to 37.5 or 41.5 MHz. PCI cards take 37.5MHz usually well, but with 41.5 MHz you may run into stability problems with certain cards.

Hope this helps.
Cheers, Jan

It also pays to note that this motherboard, as with my TX97-XE, has a known inadequate power delivery issue. They list that over on the The Retro Web site I linked in my post above.

That does not mean you're going to run into issues running faster more power hungry processors, it just means it's possible and should be aware.

In my case, I'm not running anywhere near what the board supports (that Cyrix PR166+ I mention above), but since it's a DOS 6.22 only machine, I don't need anything that fast. If I was to upgrade the processor closer to the higher-end of what the board supports, I would closely monitor it to see if it showed signs of any of those stability issues so I didn't damage my hardware.

Thank you all for the valuable info provided!!
I do not want to damage my board or cards by overclocking.
I do not know the history of this board. So I'll stick the the base clock of 66mhz for the chipset. I have a P3 system for faster needs
So what is the fastest, best performing K6 chip with a base of 66. Or could I get a K6-2+/500 and under clock it for base of 66?

A K6-2+/500 will be perfect for this TX97-E board. It will run at any Bus clock this motherboard provides and at 66MHz and a x6.0 multiplier you can reach a 400MHz CPU speed.
But be sure to flash the patched 0112e_J2 BIOS before you install this CPU.

And if you later decide to try 75 or 83 MHz afterall, this K6-2+/500 will still run within spec. 😀

Cheers, Jan