It’s typically all the security bloat and third party AV rubbish that folks think they need that messes it up under Windows.

Boot same box under Linux and it magically passes full rate.

Heaven help them if they wanted to fill a 2.5, 5 or 10 GbE pipe!

Linus tries (and fails) to break an *old* M1 Mac Mini with multiple 10 GbE 🤣

In reply to a post by jchamier:

20 years ago with a thinkpad T41 using a Pentium M CPU, I could easily manage 940 Mbps over a GigE port, with no such thing as hardware offload. A misconfigured 2.5 GbE card should dump load on the CPU, but any CPU in the last 10 years should be able to handle GigE surely?

I have nine-year-old Celeron N2820s that can also fill a gigabit without problems (using iperf3). But they are not running Windows.

Sorry for only coming back now, thanks for all the replies. I set up dual-boot Windows and Linux mint and have just tested at 940 in Mint so it looks like it's a Windows thing. I've googled optimim settings for the 2.5GB card so I think that's OK. Windows averages 600 which is well below the (BT) guaranteed speed and sometimes it's as low as 400. Upload speed is around 110 which appears to be very good. So I'm not sure if the speeds I'm getting are actual speeds or a false reading, is that possible? I'm happy enough with the speeds but I'm noit keen on paying for 900 if I'm not getting it.

Should have said I'm using the latest smart hub and have run tests direct from BT.

In reply to a post by tmarsh12345:

Sorry for only coming back now, thanks for all the replies. I set up dual-boot Windows and Linux mint and have just tested at 940 in Mint so it looks like it's a Windows thing. I've googled optimim settings for the 2.5GB card so I think that's OK. Windows averages 600 which is well below the (BT) guaranteed speed and sometimes it's as low as 400. Upload speed is around 110 which appears to be very good. So I'm not sure if the speeds I'm getting are actual speeds or a false reading, is that possible? I'm happy enough with the speeds but I'm noit keen on paying for 900 if I'm not getting it.

The speeds you are seeing are actual speeds.

The Mint test proves that BT are delivering what you are paying for.

If your Windows machine isn't sufficiently powerful to handle this speed of traffic, that is a problem with your machine and you can't blame BT for that. (You can blame Microsoft).

You could downgrade the Internet link to 300M or 500M and be perfectly content with that - but if you're already in a contract for 1G that might not be possible. (Personally I think that hardly anyone can notice the difference between 300M and 1G in normal use, i.e. without using a Speedtest site, especially on a wifi-connected device)

In reply to a post by tmarsh12345:

I'm happy enough with the speeds but I'm noit keen on paying for 900 if I'm not getting it.

If you're getting 900+ in Mint then you have no issue with BT. The problem is with your installation of Windows.

If you use third party security / antivirus / anti-malware software you may need to fully remove this, and locate any "completely remove" tool on the vendor website. Then try some of the tips at https://www.speedguide.net/ which attempt to repair some of the MS settings that third party AV tools mess up. (as even some new computers come pre-loaded).

Some of this security garbage is run by companies that are finding it almost impossible to make money, so can't invest in updating for new versions of Windows, as most corporates have abandoned third party security software.

Symantec was a leader in this, they sold to Broadcom and now Broadcom have sold that part on.... they realised they'd bought something crazy.

You need defence in depth, which means a) checking email (free if you use GMail, Yahoo, Outlook/hotmail or similar) and b) adblocker or similar in your browser, and then let the operating system's built in tools protect the operating system.

In reply to a post by candlerb:

If your Windows machine isn't sufficiently powerful to handle this speed of traffic, that is a problem with your machine and you can't blame BT for that. (You can blame Microsoft).

Ryzen i5 3600 with 32gb ddr4 ram and an nvme driove so probably OK. I'm using avast free. How does av limit speed?

In reply to a post by tmarsh12345:

How does av limit speed?

It modifies the Windows operating system in a way that MS never intended, and the software written by the small (compared to MS) number of staff company is not of the same standard, or tested to as many variables. Seen across all the consumer products, Kaspersky, Norton, AVG, Avast etc, and known for years by those whom run their own networks (copying large files / photos between machines) and now more obvious as internet speeds increase over 200 Mbps.

In reply to a post by jchamier:

In reply to a post by tmarsh12345:

How does av limit speed?

It modifies the Windows operating system in a way that MS never intended, and the software written by the small (compared to MS) number of staff company is not of the same standard, or tested to as many variables. Seen across all the consumer products, Kaspersky, Norton, AVG, Avast etc, and known for years by those whom run their own networks (copying large files / photos between machines) and now more obvious as internet speeds increase over 200 Mbps.

Interesting. Didn't realise that. I do a re-install of windows every now and then so will try without avast. So is it windows defender that I would use instead?

If you can do a fresh / clean slate Windows build all the better.

Don't install Avat. Leave it otherwise vanilla and re-run all your speed tests...