# Multicore & Parallel Processors ## What is parallel processing? - Parallel processing occurs when a computer has **multiple cores** available for use - Each core can work on the **same task** to complete it **more quickly** - Alternatively, each core can work on **separate tasks** at the **same time**

Parallel processing is the simultaneous execution of instructions across multiple processing cores

## What is multicore processing? - A multicore system has **more than one processing unit** in a single processor - These units can **independently process instructions at the same time** - Parallel processing can also be achieved by using more than one processor (e.g. a CPU working alongside a GPU)

Think of a kitchen: a single chef (single-core) must prepare each dish sequentially, while multiple chefs (multicore) can prepare several dishes simultaneously

## Benefits and Limitations of Parallel Processing | **Benefits** | **Limitations** | |--------------|-----------------| | **Speed:** If a task can be divided into subtasks that can be executed simultaneously, the total execution time can be reduced | **Limit on maximum speed:** Even with an infinite number of processors, there is a limit to the maximum speed improvement that can be made using parallel processing if a part of the program can't be parallelised | | **Improved performance:** Simultaneous computation can take place on different data subsets (this would be used in machine learning, data mining and scientific computing) | **Complex programming:** It is harder to write code for parallel processing than serial processing. Tasks have to be synchronised and data shared correctly | | **Better resource utilisation:** Parallel processing allows for better use of computer resources as multi-core or multiple processors can be used more effectively | **Debugging difficulty:** It is more difficult to debug a parallel program than a serial program due to the precise timing of specific events | | **Problem solving:** Problems which are large and complex (which lend themselves to parallel processing) can be solved more easily | **Communication between processors:** Communication between processors can take significant time and resources, potentially outweighing the benefits of using parallel processing | | **Real-time applications:** Real-time applications including graphics rendering are more feasible and will benefit significantly | **Limited applicability:** Not all tasks can be run in parallel and must be executed serially |

Not all programs benefit from parallel processing - some tasks must be completed sequentially and cannot be split across cores

## What are the benefits of using multicore processors? ### Multitasking - Each core can work on a different task - This is particularly effective when the user has multiple applications open at the same time - For example, a web browser can run on one core while a video editor renders on another core without interference ### Background tasks - When using a single core processor, a background task like system updates can slow down the user's primary task - A multi-core processor can assign the background task to one core, reducing the impact on other tasks - For instance, while downloading large files on one core, you can continue editing documents smoothly on another core

Background virus scans no longer freeze your computer when you have multiple cores handling different responsibilities

### Improved responsiveness - If a program becomes unresponsive, it won't slow the user's computer down as much when using multi-core - Other cores will continue running their tasks - For example, if a photo editing application freezes, your music player and word processor continue operating normally on separate cores