Data storage and asynchronous code

By definition, external data storage systems require asynchronous code in the Node.js architecture. The access time to retrieve data from disk, from another process, or from a database, always takes sufficient time to require deferred execution. 

The existing Notes data model is an in-memory data store. In theory, in-memory data access does not require asynchronous code and therefore, the existing model module could have used regular functions rather than async functions.

We knew that Notes must move to using databases, and would require an asynchronous API to access Notes data. For that reason, the existing Notes model API uses async functions so that in this chapter, we can persist Note data to databases.