# Concurrent Processing ## Benefits & Drawbacks of Concurrent Processing ### What is concurrent processing?

Concurrent processing allows multiple processes/tasks to run on a single processor by giving each process a fraction of time and control over the processor before swapping to another process

- Each process receives a **timeslice** - a small amount of processor time - After its timeslice expires, the processor switches to another process - This switching creates the illusion that tasks are running simultaneously - In reality, execution is sequential but happens so quickly humans perceive it as simultaneous ### Advantages and disadvantages of concurrent processing | Advantages | Disadvantages | |------------|---------------| | Increased program throughput as the number of tasks completed in a timeframe are increased. For instance, fifteen programs could be 40% complete versus three that finish entirely | If large numbers of users or processes are running that involve high quantities of computation, these processes will take longer to complete as each is allocated a certain timeslice | | Time spent waiting for user input or react to output is minimised by swapping to another task and waiting for an operating system interrupt before swapping back to the waiting task | |

Some operating system scheduling algorithms can prioritise certain concurrent processes over others, meaning larger processes could finish sooner

### Advantages and disadvantages of parallel processing | Advantages | Disadvantages | |------------|---------------| | When performing repetitive calculations on large quantities of data such as image or video editing, parallel processing can speed up performance by splitting processes over several processors | Different processors running programs simultaneously may need to communicate, leading to overhead and delays on processing | | Graphical processing units can render 3D objects quickly by splitting the computations of a scene between multiple cores | Some tasks may run faster or may be optimised to run on a single processor rather than multiple processors | | Multiple different programs or browser web pages can run on different processors at the same time | | ## Worked Example: Flight Simulator **Scenario:** A flight simulator allows a user to take control of a simulated aeroplane. The user can fly the plane in an environment that can simulate different weather conditions and additional planes in the sky. **Question:** Explain what is meant by 'concurrent processing' and describe one example of how the simulator could make use of it. (4 marks) **Answer:** Concurrent processing is where multiple processes are allocated timeslices of processor time and are pipelined to allow multiple processes to make progress in the same time frame. **[1]** **Example:** An example of concurrent processing in a simulator would be the plane moving independently of other planes or weather conditions **[1]**. Individual planes or weather do not always interact with each other allowing them to operate separately **[1]**. This allows multiple objects and events to occur in the program "at the same time" and react to different events **[1]**

Remember to state your example, say how it acts concurrently and why it is necessary that it is concurrent

## Key Points to Remember - **Concurrent processing** = multiple tasks on a single processor using timeslices - **Parallel processing** = multiple tasks running simultaneously on multiple cores - Main advantage: better resource utilisation and increased throughput - Main disadvantage: computationally intensive tasks take longer due to time-sharing - Consider dependencies when determining what can run concurrently - Communication overhead can reduce the benefits of parallel processing