Real parallelism refers to the simultaneous execution of multiple instructions or tasks on multiple processing units (cores, processors, or even specialized hardware). This means that the instructions are truly being executed at the same time, leading to genuine speedup.
Key characteristics:
* True concurrency: Instructions from different tasks are executed concurrently.
* Multiple processing units: Requires multiple physical processors or cores.
* Faster execution: Achieves significant speedup for tasks that can be divided into parallel components.
Example: Running a complex simulation on a multi-core processor, where different parts of the simulation are executed on different cores simultaneously.
Pseudo-Parallelism
Pseudo-parallelism, also known as simulated parallelism, involves the illusion of parallel execution but doesn't actually run multiple tasks at the same time. Instead, it uses techniques like:
* Time-slicing: Switching rapidly between different tasks, giving the appearance of parallel execution.
* Interleaving: Executing instructions from different tasks in an alternating fashion.
* Pipelining: Breaking down instructions into smaller steps and processing them in a pipeline, overlapping execution.
Key characteristics:
* No true concurrency: Only one task is actually executing at any given moment.
* Single processing unit: Can be achieved on a single processor or core.
* Limited speedup: Speedup is limited by the time spent switching between tasks or the overhead of pipelining.
Example: A single-core processor running a multitasking operating system, where multiple programs appear to run concurrently but are actually time-sliced.
Difference between Real and Pseudo-Parallelism:
| Feature | Real Parallelism | Pseudo-Parallelism |
|-------------------|-------------------|--------------------|
| Concurrency | True | Simulated |
| Processing Units | Multiple | Single |
| Speedup | Significant | Limited |
| Examples | Multi-core CPU, GPUs | Time-slicing, pipelining |
In summary:
* Real parallelism provides true concurrency and significantly faster execution by utilizing multiple processing units.
* Pseudo-parallelism simulates parallelism using techniques like time-slicing and pipelining, but doesn't achieve true concurrency and offers limited speedup.