New England Data Services Blog

What Is Cache?

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So you’re sitting at your desk to doing some work. You are just about to sign a contract, but there is no pen on your desk. Remembering that the company keeps all the pens 3 floors down in the warehouse, you jump up to go get one. Finally, you arrive back at your desk with a pen, sign the contract and return the pen to the warehouse. Ten minutes later, another contract comes in and you need the pen again. Now you have to go back down 3 flights of stairs, get the pen, and bring it back to your desk. I get tired of people explaining how computers work with all the technical terms, so I will continue to use this office situation throughout this explanation.

Essentially, this is how a computer works between the guy working at the desk (the CPU) and the warehouse (RAM) where your necessities are stored. Unfortunately, the design of a computer does not allow the RAM to be right next to the CPU. When the CPU must perform a task, a signal has to travel from the CPU to the RAM, locate the desired action or information stored in a memory location, and bring it back to the CPU where it is processed. Wouldn’t it be nice to have a storage place right on the desk to keep pens?

Cache is a small memory system built right on CPU to eliminate the need to travel to the RAM for frequently used processes or information. Cache is a very small size and does not hold large files. A small and frequently used process like adding two numbers is a task that can be stored on the cache. In our office example, something like a pen could be stored on our desk (cache) because of its small size and frequent use.

Sometimes your desk just gets too cluttered and you need to clean it off. This occasionally needs to be done with cache memory. Filling up your cache slows your computer down and makes it so the CPU has to travel all the way back to the RAM again. If your desk is filled up, you can’t really find anything and you have to go back to the warehouse to get another pen.

You may be asking why the cache doesn’t just store all of the information of the computer so RAM is not needed, right? The reason is that cache is very expensive. In other words, we use the small amount of cache to speed up the larger amount of RAM. In other words it is much cheaper to use a warehouse for storage than buying desks to fit everything in your warehouse.