Cache

What is a Cache?

A cache is a special storage space that keeps copies of data that’s frequently used or takes a long time to get.

By keeping this data in a faster, closer location, computers can work much more quickly when they need that information again.

Simple Analogy

A cache is like a notepad you keep next to you while studying:

• When you look up an important formula in your textbook, you write it on your notepad
• The next time you need that formula, you check your notepad first
• If it’s there, you save time by not having to flip through the textbook again
• If it’s not there, you look it up in the textbook and add it to your notepad
• Since your notepad is small, you might need to erase old notes to make space for new ones

Types of Caches

• Browser Cache: Stores web pages, images, and files you’ve visited
• CPU Cache: Ultra-fast memory built into the processor (L1, L2, L3 caches)
• RAM Cache: Keeps copies of disk data in memory for faster access
• DNS Cache: Remembers which domain names go with which IP addresses
• CDN Cache: Stores copies of website content at locations around the world
• Application Cache: Custom caching systems built into software

Key Cache Concepts

• Hit: When requested data is found in the cache
• Miss: When requested data isn’t in the cache and must be fetched from the original source
• Eviction: Removing items from the cache to make room for new items
• Cache Policy: Rules that determine what gets cached and for how long
• Warm Cache: A cache that already contains useful data
• Cold Cache: An empty or newly started cache

Example

When you visit a website like Wikipedia, your browser downloads all the images, CSS files, and JavaScript files.

If you click to another Wikipedia page, your browser doesn’t need to download those files again - it can use the copies in its cache. This makes the second page load much faster than the first one.