If two engines process four submitted jobs at the same time, what happens?

• A. Two processed, two sit in a queue until an engine is free.
• B. Two jobs are processed. The other two sit in a queue until an engine becomes free.
• C. Two extra engines will fire up automatically to process all four jobs.
• D. The four jobs will be processed simultaneously, sharing the two engines.

Answer: (A)

This tests how concurrency works with a fixed set of processing units. With two engines and four jobs, only two jobs can run at the same time because there are only two engines. The other two must wait in a queue until an engine finishes one job and becomes available. Once an engine frees up, it takes the next job from the queue and starts processing it. So, two jobs are processed now, and the remaining two sit in the queue until an engine is free. The idea here is that you can’t process more tasks simultaneously than you have engines, unless you scale up resources, which isn’t assumed in this scenario.