system
Given the following post, respond as if you're commenting on Reddit:
human
What causes a computer to slow down over a period of time?

At my workplace we have some computers that are about 6 years old. These computers are only ever used for word processing and browsing the Web. They are also 're-imaged' or have their hard drives effectively wiped every year at around this time. So why is it that when they were new they were lightning fast but now, even though they're running pretty much identical software and are put to a similar level of use they are terribly slow? Is it degradation of components? Common apps like IE and Office requiring more power? or something else?
gpt
From a purely web viewing perspective, a lot of web sites are pushing more work to the browser.  Where in the past a website would contain mostly static HTML, a lot more websites are making use of Javascript.

Javascript allows a browser to change the contents of a webpage after the browser has already rendered it.  For example when you view google maps you've already loaded the page that displays the map data.  But when you "grab" the map and move it in a particular direction, it automatically loads the images that need to now be shown because you've taken some areas outside of the viewing screen and added new ones.  This is all done behind the scenes with Javascript and if you notice you're still at the same "page" but the contents of the page have changed.

All this Javascript rendering and loading uses more CPU cycles.

TLDR - From a web browsing perspective as computers have gotten more powerful from a web page standpoint web sites have used more features to make web sites nicer looking and more user interactive.  Older computers have to work harder to run these new features.