Caches store copies of files to deliver websites robustly to deliver at fast speeds where they are needed for various demands.
Caching stores copies of files or data in a cache, or temporary storage location, to be accessed more quickly. Technically, a cache is any temporary storage location for copies of files or data, but the term is often used in Internet technologies. Web browsers cache HTML files, JavaScript, and images to load websites more quickly, while DNS servers cache DNS records for faster lookups, and CDN servers cache content to reduce latency.
To understand how caches work, consider real-world caches of food and other supplies. When explorer Roald Amundsen returned from his trip to the South Pole in 1912, he and his men subsisted on the caches of food they had stored along the way. This was much more efficient than waiting for supplies delivered from their base camp as they traveled. Caches on the Internet serve a similar purpose; they temporarily store the ‘supplies’, or content, needed for users to make their journey across the web.
What does a browser cache do?
Every time a user loads a webpage, their browser has to download quite a lot of data to display that webpage. To shorten page load times, browsers cache most of the content that appears on the webpage, saving a copy of the web page’s content on the device’s hard drive. This way, the next time the user loads the page, most of the content is stored locally, and the page will load much more quickly.
Browsers store these files until their time to live (TTL) expires or until the hard drive cache is full. (TTL is an indication of how long content should be cached.) Users can also clear their browser cache if desired.
What does clearing a browser cache accomplish?
Once a browser cache is cleared, every webpage that loads will load as if it is the first time the user has visited the page. If something loaded incorrectly the first time and was cached, clearing the cache can allow it to load correctly. However, clearing one’s browser cache can temporarily slow page load times.
What is CDN caching?
A CDN, or content delivery network, caches content (images, videos, or webpages) in proxy servers closer to end users than origin servers. (A proxy server is a server that receives requests from clients and passes them along to other servers.) A CDN can deliver content more quickly because the servers are closer to the user making the request.