Realtek NIC Issue ?
Realtek NIC Issue ?
An old Gigabyte GA-B85M-D3H motherboard, running Windows 10, has an onboard Realtek PCIe GbE Family Ethernet Controller. The driver rt640x64.sys Realtek 9.001.0410.2015 is installed, though no newer version is available. My new 1Gb fibre connection provides 1Gb via Cat5e from the router to the PC's RJ45 port, confirmed by the orange '1Gb' LED. However, only about 300Mb+ reaches the machine. Driver checks indicate I have the latest version. I've adjusted Flow control to 1Gbps full duplex and switched back to Auto, but it didn't work. Anyone know what could be wrong?
So there are a few things to consider.
You likely have an internet connection rated at 1gbit.
You don’t have another device available for testing speed, or you might be testing across different machines inside the house.
Either your Wi-Fi isn’t active on the device or it’s turned off completely to ensure you’re only checking Ethernet performance.
What I’d suggest doing next is obtaining a Linux boot image on a USB drive and running it. These images usually come with drivers for all standard Ethernet support and include a basic web browser ready to go. This setup should allow you to perform a speed test from Linux without affecting your Windows installation. It should help determine whether the issue lies in Windows software or something else entirely.
If you’re using a high-end Ethernet chip, I’d advise switching to alternative drivers. Such chips rarely cause speed drops. The Ethernet port itself is quite straightforward and can’t inherently restrict performance.
The main culprit here was likely the inclusion of unnecessary "gamer" acceleration within the driver. This type of software is often the most frequent source of such limitations. It’s usually bundled with extra features from motherboard or graphics card manufacturers, and Asus is frequently cited as a problematic example. Try uninstalling any programs that mention QoS or traffic prioritization.
If Linux reports the same slowdown, check your router for similar issues. Routers have built-in hardware that can bypass CPU-based checks through NAT. Any feature in the router that demands CPU involvement—like QOS, firewall, or parental controls—can disable this capability, forcing the CPU to handle NAT tasks instead.
Thank you, bill - all three assumptions are correct. I'll attempt the Linux boot. The QoS is disabled on the router. Would any of your 'killer' features display 1Gb at the RJ45?
The nic operates without issues since it always sends data at full capacity. It can transmit either 1gbit or 0gbit, depending on the situation. The observed speeds are averages over brief intervals. This ensures there’s no actual slowdown from the nic. The output on the RJ45 port will consistently show either 1gbit or 100mbps, never anything like 300mbps or 700mbps. These limits are built into the hardware, and while other devices can handle higher rates, the nic itself only supports those two options.
I'm searching for any QoS software options. Perhaps changing the browser settings could help, as it might be a peculiar configuration. You might also want to use various speedtest websites to check if the issue is linked to testing tools.
Typically I suggest running an IPERF test between two devices in your home network. This removes browser interference but requires both machines to be available.
It probably won't make a big difference, but it's worth a try.
I suspect you might not have the newest driver, yet you need the specific chipset identification.
If you visit the motherboard manufacturer's page, they list a driver starting with 10.001 from 2020.
You can also download drivers directly from Realtek, which include support for many chipsets.
This version is from 2026, though I doubt they've fully updated drivers for your chipset and don't provide clear details about the installation.
https://www.realtek.com/Download/Li...we...ltekanyway