Cache definition: a hidden stash and a speed trick

Cache definition and meaning: the senses in order

1. A hidden store. A collection of items put away in a secret or safe place: a cache of weapons found by police, a squirrel's cache of nuts, a cache of old letters in the attic.
2. The hiding place itself. Older or more technical: the spot where things are kept, such as a cache dug into the snow by explorers.
3. In computing. A small, fast memory or storage area that holds copies of data so future requests are served faster. Your phone, browser, processor and many websites all use caches.
4. As a verb. To store something in a cache: "The app caches maps so you can use them offline."

If you have to define cache briefly, the definition of cache in both everyday and technical use comes back to the same picture: a ready supply kept close at hand.

How a computer cache works

Fetching data from a distant server or a slow disk takes time. A cache saves a copy of recently or frequently used data somewhere quicker. Next time, the system checks the cache first.

• Cache hit: the data is there, so it loads almost at once.
• Cache miss: the data is not there, so the system fetches it the slow way and usually stores a copy for later.

A simple worked example: you open a news site in the morning. Your browser downloads the logo, fonts and layout files and keeps them in its cache. When you return at lunch, only the new headlines are downloaded, so the page appears faster and uses less data.

Common types include the CPU cache (tiny, very fast memory on the processor chip), the browser cache, the app cache on phones and server-side caches that store popular pages. Deciding what to keep and what to throw out is handled by an algorithm.

Why people clear the cache

A cache can grow large, hold out-of-date copies, or get corrupted. Clearing it deletes the stored copies, which can fix a page that will not update, free up storage and remove traces of browsing. The downside is that the next visit to each site or app may be a little slower, because everything has to be fetched again. Clearing cached files is different from clearing saved passwords or cookies, which most settings menus list separately.

From fur trappers to processors

English picked up cache in the late 1700s from French Canadian trappers and explorers, whose word named a hidden store of food, furs or supplies left in the wilderness to collect later. It comes from the French verb cacher, to hide, which goes back through Old French to a Latin word meaning to press together or store up. In the 1800s the meaning widened to anything kept in a hiding place. Computer engineers adopted it in the 1960s for fast memory placed between the processor and main storage, a fitting image of supplies kept close by.

Cache in example sentences

• Hikers found a cache of tinned food and matches left by an earlier expedition.
• If the website looks broken, try clearing your browser cache and reloading.
• The new laptop has a larger processor cache, so heavy apps run more smoothly.
• Archivists discovered a cache of photographs in a sealed tin box.
• Our music app caches songs on the phone so they play without internet.

Cache, cash and cachet

A common mistake is to say "cash-ay" for cache. That pronunciation belongs to cachet. Also, a "cache of cash" is fine English: a hidden stash of money. For other tech terms, try the science and technology hub or read about redundant systems and backups.