Cache to an application is like a palette to a painter. A set of data is temporarily put on the cache as the application runs, the same way a painter picks a few color to the palette as he works on the painting. Data might be combined and modified in the cache, the same the color is mixed on the palette. The cache keep some frequently used data in memory, and save the application from accessing disk drive or database all the time, which save time. The palette keeps the mostly frequently used color, and reduces painter trips to the color tub. Of course, no analog goes all the way. In this case, data does change and need to store back. But, painter doesn’t put the color back into a tub when he discovers a new color that he likes.