Does only distributed systems follow CAP theorem?

Question

I have read somewhere on the internet that the theorem is a set of basic requirements that describe any distributed system. Please help me in understanding that is the theorem only applicable to the distributed systems?

Answer 1

It applies to any system that relies on message passing for communication instead of, say, shared memory.

For most people, that means any system that communicates over a network. For many website architectures, the CAP theorem trade-offs drive the which-database-to-use decision. For example, choosing between using a big MySQL database vs DynamoDB vs all things in between.