Caching refers to the practice of saving reusable replies in order to speed up later queries. Caches can be located at any point along a content's route from the source server to the browser. Web caching works by caching HTTP answers for requests that meet specific criteria. These cached responses are called "cachers". When I make a request of a web page, my browser sends this request to the website's server. The server looks in its cache (if it exists) for an answer to send back to me. If it finds one, it sends this response back to my browser instead of sending the answer directly from itself. This saves time for everyone involved.
There are two types of web caches: proxy and forward caches. A proxy cache is used when there is no direct relationship between the server that provides the content and the server that users connect to. For example, a university may have a proxy cache at its network edge so that students can get access to resources on other campuses around the world. A forward cache is used when there is a direct relationship between the server that provides the content and the server that users connect to. For example, a company's intranet might use a forward cache so that employees can get access to resources within the company system even if they are working from home. Forward caches are more efficient than proxies because they don't need to repeat the work done by connecting users to foreign servers; they simply return responses from their own storage systems.
Caching is a method that saves a copy of a given resource and returns it when it is requested. When a web cache has a copy of a requested resource in its storage, it intercepts the request and returns it rather than re-downloading it from the original server. Caches can improve download speeds for users, reduce traffic on servers, and save money for website owners.
There are two types of web caches: transparent and opaque. Transparent caches are located between users and sources. They read resources from websites or other external files and store them in their database for later retrieval. These caches do not alter the content of resources before returning them to users. Opaque caches do alter the content of resources before returning them to users. For example, an opaque cache might replace one image with another or remove certain words from a page before returning it to users.
Transparent web caches benefit websites by storing copies of their resources, which reduces the number of requests they have to make to an origin server. This reduces the load on the server and helps ensure the integrity of resources. Users see no difference when using resources from cached versions of websites because caches do not alter the original content of resources. Caches also help users find resources on websites even if the sites suffer temporary downtime or permanent removal.
Opaque caches benefit websites by reducing the amount of data that needs to be transmitted to users.