Cluster:

• There is one process on each CPU with an IPC to communicate.
• In case we WANT to have multiple servers accepting HTTP requests via a single PORT, clusters can be helpful.
• The processes are spawned in each CPU THUS will have separate memory and node instance which further will lead to memory issues.

Worker threads:

• There is only one process in total with multiple threads.
• Each thread has one Node instance (one EVENT loop, one JS engine) with most of the APIs accessible.
• Shares memory with other threads (e.g. SharedArrayBuffer)
• This can be used for CPU-intensive tasks like processing data or ACCESSING the file system since NodeJS is single-threaded, synchronous tasks can be made more efficient leveraging the worker's threads.