Why can't old PCs view modern sites?

As of 2019, and a few years before, there's another factor. Any modern, secure site would have some flavour of TLS encryption, and be hosted over HTTPS. The browsers of yore as linked below probably would simply not be able to load many sites - even 'simple' ones without some intermediary (See this example of a slack client for windows 3.11 ).

Simply, a lot of modern HTML features we take for granted did not exist back in those days. There are attempts to build 'modern' browsers for older OSes - classilla, for example. You can easily load up linux onto a suitable PII or PIII system and still be able to handle a basic modern webpage.

On the other hand

This is google on OS/2 warp 4.52, on a VM on a modern CPU. I could replace this with linux and the same page would render correctly. If I only could find a modern browser of some sort, I'd certainly be able to render this very simple page. Opera might work

Same page, different browser (opera 5.2 I think), and it works gloriously here. It breaks down to newer browsers support far more than older ones did. If you could get a 'modern' browser to work, it might render things better - SE chat breaks down for one - and its a modern HTML5/Ajax based website.

Naturally I have neither flash nor HTML 5 there, but you get the idea. Its all about the browser

I have a 9 year old P4 desktop at home, with Ubuntu 12.04 installed. It has a 500GB hard disk, 3GB RAM, and a 512MB video card. I use it as home server, for backup, file sharing, and for batch scanning negatives. I don't know how it would work with XP now, but I suppose it would not make much difference in speed.

It can do almost anything. YouTube videos work. Some videos don't work properly, probably because the resolution is too high. Most sites work, although it takes a bit longer. Doing two things at a time may take a while... I can even start up VirtualBox and run Photoshop in it. That really works, although sometimes I have to wait several seconds. Wait for each action to complete. Close everything else, especially Firefox with heavy sites in it.

So how does this relate to your situation? This is a P4, so two generations later, but still 9 years old.

My guess is that Windows gets slower with all updates. I cannot prove that, but it's my gut feeling. JavaScript in websites is much more complex. Think of jQuery and what it can do. Browsers can handle PNG transparency. CSS3 and HTML5 require more power. Do you use add-ons? Antivirus? Antivirus from 10 years ago required less power I suppose. Now there are all these different kind of threats and the antivirus program has to scan for them.

There is not one reason. It's the whole package. Not only more memory, but faster memory. Hard drives have faster connectors.

Your old computer may need a system that requires less in the basis, like Ubuntu, Debian or Centos. Maybe that makes it more acceptable, but maybe it doesn't make much of a difference. You can only try. Ubuntu is the most fancy for desktop usage, the others have less bells and whistles, but do the job.

Modern browsers are optimized for maximum speed, not for minimum memory usage. Hence, 1Gb+ RAM requirement is pretty much common these days, at least for comfortable browsing with 5 or more open tabs/windows.

Old computers just don't have that much RAM.

I think the answer depends a bit on what you mean by "view". I can view the text and graphic content of most sites with links2 -g on a 10-year-old Dell running Xubuntu.

All of the fancy css formatting is gone but once you get used to the default layout, it is very readable.

The only sites that don't work are those that block access by older browsers (e.g., Facebook, Trello, etc... I assume this is a JS issue)

To answer your question, the content of most modern websites can be viewed on old PCs but you may not be able to see the formatting or use interactive features.