Archive relates to historic or previous versions of a website, even websites which may no longer be online, so archive sites can be really useful when researching online sites
Cached Pages relate to copies of a webpage, usually held by a search engine from the last time it visited the webpage, so can be useful when researching sites which may have recently changed or been taken offline
Useful Details & Articles To Help You Investigate Using Archive Sites
Cached Pages
Google killed off and removed its Cached functions, followed by Bing & Yahoo, so really that only leaves Yandex who still display its Cached results, >, where it is referred to as Saved Copy.
Firefox Add-Ons For Archive & Cached Related Tasks
Chrome Extensions For Archive & Cached Related Tasks
Website Copiers & Downloaders
Website Copiers & Downloaders From Archive.Org
Website Scrapers
Webpage Date & Time
Not an add-on or extension but we demonstrate this on our course and it is a little useful tool, so if you want to save this feature to your Favorites or Bookmarks right click on Web Page Date and then click on "Add To Favorites" or "Bookmark This Link", or just left click on the Web Page Date link and then drag it to your Favorites bar, to assist in showing when a static webpage was last updated