I actually installed Windows 98 on a Z790 DDR5 motherboard with a Realtek 8125 2.5Gbit LAN. The NDIS 2 driver initialized successfully the card in DOS, but it didn’t seem to work in Windows 98. Maybe I didn’t try hard enough, I gave up after a few restarts.

Anyway, for PCI-E Gigabit LAN in Windows 98, you should focus on Broadcom NetXtreme 57xx cards. I recently tested two such cards: a BCM95761 model from 2010, which didn’t work, and a BCM95722 from 2008, which worked perfectly fine. The model numbers make no sense - the 5751 cards are older than the 5722 ones, for example. So, if you’re planning to grab one from eBay, pay attention to the manufacturing date. The driver is from 2006, so the closer to that date, the better.

Btw, you can see these two Broadcom cards installed on Windows 98 (along a Quadro FX4500) on this video.

I have an Intel Pro1000GT in my 233MMX system simply because that's what I had on-hand. There are 98 drivers for it and they work fine, so that's another Gig-E option for 98 folks.

Support and speed are two different things under Win9x or XP 🤣.

Tweaking the TCP receive window largely fixes the speed issues under XP, the NT/2k/XP TCP stack is pretty decent actually. Win9x... well, it sort of manages to push packets over the network 😉

As for the use case for a 2.5GbE adapter - I'd say it's purely relevant for trying to install Win9x on hardware that already has one, doesn't have space for a second, more easily supported adapter and/or needs to dual-boot with something modern. Tbh, I'd just run Win9x in a VM on such modern hardware if I really wanted to, but others apparently relish the challenge of getting it to work on bare metal never intended to run it.

Sorry for the necroposting, but the 2.5gbps NDIS2 driver works absolutely fine on my end.

Using my script tooling from Win98 QuickInstall, here is a driver bundle with the appropriate 9x-style INF file.

Install iperf and see how it actually performs!

Not well 😀 But that's the 98SE network stack for you.

Oerg866 wrote on 2026-09-25, 17:33:

Sorry for the necroposting, but the 2.5gbps NDIS2 driver works absolutely fine on my end.

Using my script tooling from Win98 QuickInstall, here is a driver bundle with the appropriate 9x-style INF file.

A worthwhile necropost, IMHO, thank you.

While I do not expect I will ever need to do that, it is very good to know it can be made to work with that Realtek chip.

Oerg866 wrote on 2026-09-25, 18:58:

Not well 😀 But that's the 98SE network stack for you.

How bad is it ? I am not expecting miracles and, if it performs in the ballpark of even a 100Mbps NIC with native Windows 98 drivers, I would think it might qualify as a small miracle.

I also highly recommend Win98 QuickInstall, my HP Netbook Mini 110 has a PCIE network card and no offical Win98 support but the QuickInstall NDIS drivers work perfectly.

Oerg866 wrote on 2026-09-25, 17:33:

Sorry for the necroposting, but the 2.5gbps NDIS2 driver works absolutely fine on my end.

Using my script tooling from Win98 QuickInstall, here is a driver bundle with the appropriate 9x-style INF file.

It clearly tells 1000Mbps link speed on the command prompt screenshot.

Do you have a 2.5Gbps on the other end of the cable?

Also, there's a new Intel Gigabit driver made for 98, which seems to be very fast with an I217-LM controller (PCIe, 2013).

It was made by Daniel from sdz-mods.com, the same guy who can design something like an MXM Voodoo 5 and other crazy stuff.

These are some pictures he sent me a while ago. It was mainly made to work on his Dell M4800 (Intel Haswell, 4th Gen), but probably it's not limited to that.

OMORES wrote on 2026-09-26, 18:25:

Also, there's a new Intel Gigabit driver made for 98, which seems to be very fast with an I217-LM controller (PCIe, 2013).

It was made by Daniel from sdz-mods.com, the same guy who can design something like an MXM Voodoo 5 and other crazy stuff.

That just made my Ultimate 98/XP ITX system possible. Thanks Omores for posting that. I'm going to post in Daniels thread to thank him.

Have you heard anymore about the 1080ti working in XP from your last video?

The Solutor wrote on 2026-09-26, 14:08:

Oerg866 wrote on 2026-09-25, 17:33:

Sorry for the necroposting, but the 2.5gbps NDIS2 driver works absolutely fine on my end.

Using my script tooling from Win98 QuickInstall, here is a driver bundle with the appropriate 9x-style INF file.

It clearly tells 1000Mbps link speed on the command prompt screenshot.

Do you have a 2.5Gbps on the other end of the cable?

No? My home network is gigabit and it works fine with this chip and driver. I don't see a reason why it wouldn't on a 2.5gbps network.

Oerg866 wrote on 2026-09-26, 22:37:

No? My home network is gigabit and it works fine with this chip and driver.

Then this is why the link is at 1000Mbps, in your actual scenario

But there is a possibility that 98's drivers manage the card as an older one with 1000Mbps only capabilities, a good indication would came from the NIC advanced settings, you should have the option to force 1000 and 100 MBps speed, if the card is seen as a 2.5Obps.
If, instead you see only the option to force 100 Mbps the card is very likely taken as a 1Gbps.

What does that have to do with anything at all, the question was whether the rtl8125 2.5gbps card can be made to work with win9x using the NDIS2 driver which it clearly can. What does that have to do with the link speed?

Oerg866 wrote on 2026-09-27, 08:02:

What does that have to do with anything at all, the question was whether the rtl8125 2.5gbps card can be made to work with win9x using the NDIS2 driver which it clearly can. What does that have to do with the link speed?

Hey, relax! I assume that if someone asks for a 2.5 GBps is because he want something that reaches that speed, as odd as the request may sound for a Win9x system.

Aside that, was just easier (and helpful for who reads this thread) to check what I suggested rather than switching in upset mode for no reason.

“Working in a degraded capacity” is not the same thing as “working”.

The Solutor wrote on 2026-09-27, 08:14:

Oerg866 wrote on 2026-09-27, 08:02:

What does that have to do with anything at all, the question was whether the rtl8125 2.5gbps card can be made to work with win9x using the NDIS2 driver which it clearly can. What does that have to do with the link speed?

Hey, relax! I assume that if someone asks for a 2.5 GBps is because he want something that reaches that speed, as odd as the request may sound for a Win9x system.

Aside that, was just easier (and helpful for who reads this thread) to check what I suggested rather than switching in upset mode for no reason.

One reason to want to use a 2.5G NIC with Windows 98 is because that happens to be what one has on hand (i.e. integrated NIC, for example). Reaching the maximum performance that the hardware is capable of is not always a prerequisite. I can easily imagine a scenario where someone boots a computer into multiple different OSes, including Windows 98, and would be quite happy to have network connectivity in all of them using the same NIC.

Not everyone who happens to choose a given motherboard with an onboard 2.5G NIC will necessarily be operating the NIC at 2.5G. I, for one, would not avoid purchasing a motherboard that happens to have an integrated 2.5G NIC just because I did not have the ability to use it at 2.5G . I suspect that I am not alone.

Windows 98's networking performance is lackluster even with native drivers. While tweaking and using a massively overkill CPU can likely offset that to some degree, I doubt that one can expect to reach even 1 Gigabit effective throughput, regardless of whether the link speed is 1G or 2.5G (I would love to be proven wrong on that point, not because I need that kind of speed under Windows 98, but because I am curious about how far Windows 98 can be pushed on the front).

Finally, to paraphrase a rather famous ( in some circles ) quote, an NDIS2 driver with Windows 98 should be considered a "connectivity solution" rather than a performance-oriented option.

In other words, and at least IMHO, getting a 2.5G NIC working in an OS that reached EOL more than 10 years before said NIC was released is a worthwhile purpose in and of itself. Any fault in its performance, unless it happens to make it unusably abysmal, is, again IMHO, a truly secondary concern.

EDIT: Corrected an obvious error affecting meaning in the last sentence.

darry wrote on 2026-09-28, 05:22:

One reason to want to use a 2.5G NIC with Windows 98 is because that happens to be what one has on hand (i.e. integrated NIC, f […]
Show full quote

The Solutor wrote on 2026-09-27, 08:14:

Oerg866 wrote on 2026-09-27, 08:02:

What does that have to do with anything at all, the question was whether the rtl8125 2.5gbps card can be made to work with win9x using the NDIS2 driver which it clearly can. What does that have to do with the link speed?

Hey, relax! I assume that if someone asks for a 2.5 GBps is because he want something that reaches that speed, as odd as the request may sound for a Win9x system.

Aside that, was just easier (and helpful for who reads this thread) to check what I suggested rather than switching in upset mode for no reason.

One reason to want to use a 2.5G NIC with Windows 98 is because that happens to be what one has on hand (i.e. integrated NIC, for example). Reaching the maximum performance that the hardware is capable of is not always a prerequisite. I can easily imagine a scenario where someone boots a computer into multiple different OSes, including Windows 98, and would be quite happy to have network connectivity in all of them using the same NIC.

Not everyone who happens to choose a given motherboard with an onboard 2.5G NIC will necessarily be operating the NIC at 2.5G. I, for one, would not avoid purchasing a motherboard that happens to have an integrated 2.5G NIC just because I did not have the ability to use it at 2.5G . I suspect that I am not alone.

Windows 98's networking performance is lackluster even with native drivers. While tweaking and using a massively overkill CPU can likely offset that to some degree, I doubt that one can expect to reach even 1 Gigabit effective throughput, regardless of whether the link speed is 1G or 2.5G (I would love to be proven wrong on that point, not because I need that kind of speed under Windows 98, but because I am curious about how far Windows 98 can be pushed on the front).

Finally, to paraphrase a rather famous ( in some circles ) quote, an NDIS2 driver with Windows 98 should be considered a "connectivity solution" rather than a performance-oriented option.

In other words, and at least IMHO, getting a 2.5G NIC working in an OS that reached EOL more than 10 years before said NIC was released is a worthwhile purpose in and of itself. Any fault in its performance, unless it happens to make it unusably abysmal, is, again IMHO, a truly secondary concern.

EDIT: Corrected an obvious error affecting meaning in the last sentence.

All reasonable...

BUT

1) W98 in 2026 and modern HW, is still something that one does more as a challenge and a proof of concept rather than practical reasons. and in that logic, getting the best of any HW is part of the game.

2) even if the practical reasons to reach the full speed are close to zero, still there is a chance that 98 gets say 25% of the full theoretical speed, and 25% of 2.5Gbps is better than 25% of 1Gbps.
Personally, I'm used to install the obvious DUmeter as the first program in any windows since the day I got my first internet connection in 1998, using a cellular phone , which at the time reached 1.1kBps (9600 bps), but the byproduct of that is that I have a clear a clear vision of what any network device can do in various scenarios and OS.

3) Speaking of my question here, even if it was a stupid question (which clearly it wasn't), was not a reason to get that kind of harsh reply.
But we know that too much people tent to use forums and social networks, as a valve for their everyday frustrations in real life...