Concurrency vs Parallelism in Swift

The Mental Picture

Imagine a restaurant.

There are:

2 Cooks
2 Orders

Concurrency

One cook can switch between orders:

Cook
 │
 ├── Order A
 │
 ├── Order B
 │
 ├── Order A
 │
 └── Order B

The tasks are making progress together, but not necessarily executing at exactly the same instant.

Parallelism

Now there are two cooks:

Cook 1 ─────→ Order A

Cook 2 ─────→ Order B

Both orders are actually being worked on simultaneously.

So:

Concurrency → Multiple tasks in progress
Parallelism  → Multiple tasks executing simultaneously

2. What Is Concurrency?

Concurrency means that a program can manage multiple tasks whose execution overlaps in time.

For example:

Task A: ███     ███
Task B:    ███     ███

The system can switch between them.

In Swift, concurrency can be expressed using:

Task {
    await loadUser()
}