What is cache?

Cache (also known as “browser cache” or “Web cache”) is a temporary storage area on your device that holds copies of frequently accessed webpages, images, and other online content. Allowing your browser to store some data about previously visited websites prevents the need for future requests, and helps those sites / pages load faster the next time you visit.

Why do browsers use cache?

Caching saves time and bandwidth, by letting your browser avoid repeatedly downloading parts of a webpage that rarely or never change.

When your browser requests a webpage from a Web server, the entire page doesn’t come back as one single chunk of data. What comes back is HTML—just the text of the page, plus URLs to things like images, videos, or the code that makes interactive parts of the page work. Your browser makes separate requests to those URLs to get the images, videos, and so on.

Some of those parts—for example, the logo on a company’s webpage—never change, or stay the same for many years. Instead of downloading the logo every time you visit the page, your browser downloads it once, stores it in cache, and uses the stored copy the next time you visit the page.

Does cache take up space on my device?

Yes, but your browser will make sure that the space taken up by the cache stays under a certain limit. Once the cache reaches that size limit, the browser will delete the oldest items from the cache to make room for new ones.

Webpages can also set a “time to live” (TTL) for each part of the page, which specifies how long that part should stay cached. After the TTL has elapsed, the cached item “expires,” and the browser deletes it from the cache.

What does “clearing cache” mean?

Clearing your cache means to delete everything in it. All browsers have a way to do so, in their settings.

If a webpage is displaying strange formatting or showing the wrong images, clearing your cache may fix it. Those problems can be an indication that the webpage has misconfigured the caching of its content.

Clearing your cache won’t log you out of any sites, and it won’t clear your browsing history. If you want to keep your browsing activity private, you should use a private (incognito) window. In addition to clearing history and logging you out of all sites (by clearing cookies), private windows keep a cache separate from non-private windows, and clear it automatically when you close the window.

Other types of caching

The general technique of caching—storing the result of a time-consuming operation for repeated use—is used in several other contexts in computing.

  • You may see references to L1, L2, or L3 cache. These are small storage areas in a device’s processor that are used to speed up the device’s memory.
  • Operating systems use the device’s memory to cache the contents of on-disk files, to speed up access to those files.
  • Websites often use caching on their servers—special-purpose computers with huge amounts of memory—to both speed up the site and reduce the workload of their databases.

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