Several different files are stored on Rodney's computer desktop, each immediately accessible. Because he is actively working on them, and because he can open them whenever he wants, these files are similar to the kind of information held in memory.

The answer is working memory.

Explanation:

Working memory refers to a system which holds information that can be manipulated. The main difference between working memory and long-term memory is that the former allows the information to be modified and used in different contexts, while the latter simply stores it.

An example of working memory in use is solving math problems. The formula is stored in the long-term memory, but its application is in charge of working memory.