What is the difference in execution speed between sequential and parallel approaches?

The sequential approach performs tasks one after another, which means that the total time is equal to the sum of all individual operations. The parallel approach allows multiple tasks to be executed simultaneously, significantly reducing the overall execution time, especially if the tasks are independent.

For example, if you have 4 tasks each taking 1 second:

• Sequential: 4 tasks × 1 second = 4 seconds
• Parallel (on 4 cores): approximately 1 second

In iOS, GCD (Grand Central Dispatch) is often used for parallelism:

let queue = DispatchQueue.global(qos: .userInitiated)
for i in 1...4 {
    queue.async {
        print("Task \(i) is executing")
        // simulate work
        Thread.sleep(forTimeInterval: 1)
    }
}

Thus, the parallel approach improves the performance and responsiveness of applications, especially when executing independent tasks.