The best answer that I can offer is… maybe.
I’ve talked about having lots of tabs open in the past. Without a doubt, it can definitely impact the speed of your PC. The network, on the other hand, is possible, but a little less clear.
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PC-impacting technologies vs data across the network
The real question is what are those web pages doing on the network.
As an extreme example, let’s say that those 50 tabs were all in the process of downloading YouTube videos. That’s the equivalent of having 50 PCs all watching YouTube at the same time. That’s a lot of data across your network and it could certainly have an impact.
At the other end of the spectrum, displaying a simple web page – perhaps even like this one – should have little to no network activity after it’s completed loading. Ten, 50 or even 1000 such pages open at once – should your PC even be able to do that – should have no impact on your network.
The real issue is probably somewhere in between. With lots of web pages open, depending on what sites are being viewed some of those tabs may, in fact, be engaging servers on the net. Even simple sites, like Gmail, are constantly checking their web servers for new mail, for new ads to display, to see if you’re available for chat, to see who’s logged in and logged out, and other tasks. If you have 50 open tabs doing internet-related stuff, then it could add up.
I can’t really say for certain that this is what’s happening.
If you opened 50 static web pages that aren’t doing anything on the internet, then that’s not going to impact your network speed. On the other hand, if you’ve got a mix of things that are doing internet activity and you’ve got 50 of them, it could add up. I just can’t prove it.