It's the 3 GB Windows 10 Anniversary Update (https://blogs.windows.com/windowsexperience/2016/08/02/how-to-get-the-windows-10-anniversary-update/). You can delay it for a few months, but you can't refuse it. It's all automatic and required in Windows 10.
It might be better to visit a friend with a fast Internet-connection and make that bootable USB-stick to install it.
With me at home (a 40 mbps connection) a 3 GB download takes half an hour at most.
I use two computers, an Apple Mac for all my on-line work and a PC running Windows 10 for gaming and photos etc. Both run through a BT Broadband router on the usual abysmal BT broadband speed, so I need every byte of speed that I can get. I've noticed a lot recently that when I turn the PC on, the broadband speed on the Mac drops to almost zero - pages won't load etc. When I turn it off, the connection resumes. The last time this happened I realised that the PC was downloading updates, simply because I got the message that the PC had downloaded updates - yet there was absolutely no notification that this was happening, and checking task manager revealed no activity that would have slowed the connection. I know that the world and his wife are updating on my PC every time I switch it on - iTunes, Steam, iPod software, Windows 10 etc etc, so how do I find out exactly WHICH is doing it when I need the speed, and stop it without having to turn the PC off or leave it running overnight or when away? It may seem a minor thing but my speed is so slow the iPod update for example takes about eight hours, and when multiple programmes are updating I either have to do without web surfing for hours, or turn the PC off completely - and this seems to be EVERY time I turn the PC on at present. Can anyone tell me how to check which programme is doing it, so I'll know whether to stop it or to leave it running?

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