What is "cache"?

In everyday language, a cache refers to a hiding place to store goods. When it comes to computers, think of a cache as an out-of-the-way place to store recently used data that might be needed again.

One example is a computer's RAM cache, which is a hardware subsystem that stores the most recently requested contents of actual RAM. The CPU can access data from the RAM cache faster than from actual RAM. The computer keeps a copy of recently used RAM data in the RAM cache. When the CPU needs data from RAM, the RAM cache will first try to provide it.

Another example of cache (and the one that Cache Killer deals with) is a web browser's disk cache. When you browse the web, every word, image, sound, java applet, etc. is stored on your hard drive in the browser's disk cache. By doing this, a browser can avoid having to reload content from the Internet when you press the Back button or go to a site in the History list.

There is a limit to the size of any computer data cache. A RAM cache is generally just a fraction the size of actual RAM. (A standard Power Macintosh G3 comes with a 0.5MB RAM cache and 64.0MB of actual RAM.) Similarly, a browser's disk cache is only a fraction the size of the total amount of data viewed on the web. Only the most recently used data is stored; older data is purged from the cache.