Slow internet on one computer makes the internet slow on others?

[Bonny]

Maybe that computer have some program like utorrent, bittorrent or some proram that use internet contantly. Even if you do not download torrent, but torrent application is running, internet can be slow. Check if that computer have some torrent client that start automaticly after startup and try to turn off torrent client to see. Otherwise, also other applications can use internet all the time or you have some virus on that comuter.

Wifi router separate internet to all connected devices and if one device use internet, internet is slower also to other connected devices. All devices share same internet connection