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Caching 101. Take control of your cache

Those of you who are savvy in the world of the web have probably run across the phrase 'clear your cache' at some point, whether it was to clear out your browser history or to fix a website display issue. But those of you who use the web more casually may not be familiar with the term, and even some self-professed experts can use a bit of additional clarity on the subject.

So what is a cache?

As you might expect from the name, a cache is a set of stored information that can be used at a later time. In this context, it describes a set of files that your browser has downloaded in order to display a website, including all the necessary code, images, text, and even video segments. The browser keeps a copy of these files even after you've left the website, so that the next time you visit it you'll be able to access the website much faster.

Each file in a cache comes with a brief instruction from the website that tells your browser how long it should keep the copy before it's out of date. Once this time limit expires, the browser will check the web server to download a new copy of the file. This ensures that you won't be looking at an outdated version of the website, but sometimes the system can make a mistake and you'll need to know how to clear your cache and force the browser to download a new copy of the data.
 
Why use caching?

No matter how fast our internet becomes, at some point your browser still has to talk to the server hosting a particular website in order to ask it for information. Individually this is no problem, but when hundreds of thousands of browsers are asking for the same information simultaneously, the process can slow down dramatically. Caching is designed to speed things up by keeping a copy of the website's files on your computer, and then using that copy to display the site for as long as the copy stays 'fresh'. Instead of redownloading every part of a website every time you visit it, your browser simply checks to make sure the copy it has downloaded is still valid, and updates any parts of the site that have changed.

For most websites, especially those which are fairly static in terms of their content, this can make web browsing seem much faster to the user. It doesn't do quite as good a job when it comes to websites that are constantly updated with new content such as Facebook or Twitter, but it still can speed up certain aspects of more dynamic sites.

 
Caching on Mobile

Caching isn't just something that happens on your computer. It's especially useful for people browsing using the data plans on their mobile phones, as they don't need to use up their limited transfer quotas by re-downloading content that hasn't changed.

Your browser isn't the only thing that caches data - some apps make use of the system too. Netflix recently debuted a 'Download' feature that allows users to make a temporary copy of a show or movie on their phone using a cache, which is then deleted after a predetermined amount of time. Music streaming service Spotify also uses a caching system to ensure that your favourite song isn't interrupted if you temporarily lose your data network connection.
 
When Caching Fails

Caching is a great system, but it does have some issues. Occasionally, the cached data your browser stores can be corrupted, or the header instructions that tell your browser when to look for a fresh copy may be configured incorrectly. This can lead to display errors and other issues as your browser tries to reconcile different versions of the various files required to properly display a website.

There is also the question of privacy. When a browser saves a cached copy of your visited sites, it can act like a guide showing where you've been on the web. If you've been accessing any site that has any of your personal information such as Facebook, your email or your online banking, you may be leaving traces behind that an unscrupulous co-worker or hacker may want. Clearing your cache regularly will help prevent this from happening, as well as freeing up additional space on your device.

 
How to Clear Your Cache

Depending on which device and browser configuration you're using, there are different ways to clear your cache, but the general principles are similar. Here's a step-by-step walkthrough for some of the most popular browsers and mobile devices.

Quick Tip: If you just want to clear the cached files for a specific webpage, it is possible to quickly perform what's known as a 'hard refresh'. Click the 'reload' button while holding down the Ctrl key, or press Ctrl + F5 to perform a hard refresh in Chrome, Edge and Internet Explorer. For Firefox and other Mozilla browsers, use the Shift key instead of Ctrl. This won't clear your cache for other websites or even other pages on the same site, but it can be a great way to clear small display errors by forcing your browser to get a new copy of all necessary files from the server.

Clearing Your Cache in Chrome:

Access your browser settings by clicking the triple dot button in the top right corner and choosing 'Settings'. At the bottom of the Settings window, choose 'Show Advanced Settings', and then scroll to find the Privacy section and click 'Clear browsing data'.

In typically flippant Google style, the 'Clear browsing data' dialog box allows you to "Obliterate the following items from:" and then a choice of time period. You can choose to clear your browsing history among a range of other options, including 'Cached images and files'. Check as many boxes as you need, and click 'Clear browsing data'. The next time you visit a website, you'll be loading a fresh copy of all data from the web server.

Clearing Your Cache in Microsoft Edge:

Click the triple-lined 'Hub' icon in the top right, then select the History section. Choose 'Clear all history', and you'll be presented with a series of options similar to those found in Chrome. Check the box beside 'Cached data and files', and click 'Clear'. 

Clearing Your Android Cache:

If your apps are acting up (here's looking at you, Netflix!) or taking up too much space, you may need to clear their caches. Open the Settings app, and find the 'Apps' section. Tap the entry for the app that's having issues, and then tap the 'Storage' section for that app. Select the 'Clear Cache' button, and the next time you open the app it will re-download any information it needs to function properly.

Each device maker usually puts their own spin on Android, so your process may vary slightly, but the general principle is the same across all Android devices.

Clearing Your iOS Cache:

For those of you in the Apple software ecosystem, the only way to clear an app's cache is to delete it and re-download it. Open the 'Settings' app, then tap 'General', then 'Storage & iCloud Usage'. Choose 'Manage Storage', and then find the app that's causing problems. From there, you can delete the app and reinstall it to clear out any cached files. Just be careful, because you may delete files you wanted to keep!

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Posted by Adrian Teasdale, Tuesday 20th June 2017

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