Cache Definitions
I aim to explain the definition of a cache in the context of computer science. The situation is an encyclopedia intended for an audience with no technical background.
Parenthetical Definition: Fast and small data storage.
Sentence Definition: A cache is a data storage found in software and hardware with both fast access and a small size relative to other larger, slower storage devices. Therefore, a cache usually cannot hold all the data needed by the user, and acts as a fast intermediary storage that can hold commonly used or important data.
Expanded Definition:
A cache is a data storage found in software and hardware with both fast access and a small size relative to other larger storage forms. This definition aims to explain how they are used, their required components, visualization, and common uses.
How Are They Used?
Caches are used in a lot of different ways in software and computers, but they all follow the same general principle. There is an inherent tradeoff between size of storage and its speed of access. For example, a disk drive tends to be a lot larger and slower to access than physical memory, which is a computer storage device that is only used by currently opened programs and is quite fast. Hence, physical memory is a cache for disk drives, as although it may not be able to hold all the data the user needs due to its limited size, it can speed up subsequent or repeated data retrievals of the open programs thanks to its relatively fast access times (Beal). Therefore, caches exploit this storage hierarchy to offer increased computer performance. The diagram below illustrates some examples of storage devices in this hierarchy; each item is a cache for the one above it (Jain).
Common Cache Components
There are a couple of common characteristics between caches. Firstly, due to their limited size, many feature an eviction policy, which chooses which pieces of data to remove from the cache to make space for new data when it is full. Examples of policies include evicting data that is least recently used, least frequently used, or even randomly selected. Additionally, Caches almost always have metadata, which is data that describes the cache and the data it currently holds. This often includes information that supports the selected eviction policy, such as a count for each data item to determine which one is used least frequently. But it can also include information about the location that the data was retrieved from in the secondary larger storage device.
Notable Applications
Caches are used everywhere in computing; here are a few examples: Website browsers use caches to temporarily load images and important website data faster; most computers’ central processing unit (CPU), the hardware component that handles the execution of all your program and operating system’s code, has multiple layers of very small, but fast caches (“What Is Cache?”); and some software algorithms use caches to avoid having to perform the same calculations repeatedly.
Conclusion
Caches are a critical concept in computing and are hence ubiquitous. Without them, software, websites, and computers would perform a lot slower, so it’s useful to be aware of it.
Works Cited
Beal, Vangie. “Cache.” Webopedia, EWeek, www.webopedia.com/TERM/C/cache.html.
Jain, Rishabh. “Memory Hierarchy Design and Its Characteristics.” GeeksforGeeks, GeeksforGeeks, 17 Dec. 2018, www.geeksforgeeks.org/memory-hierarchy-design-and-its-characteristics/.
“What Is Cache?” Computer Hope, Computer Hope, 11 Oct. 2017, www.computerhope.com/jargon/c/cache.htm.
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