Amdahl’s Law

Definition of Amdahl’s Law

Amdahl’s Law, named after computer architect Gene Amdahl, is a formula used to estimate the performance improvement potential of a computing system when only a portion of the system is optimized. It states that the overall speedup is limited by the fraction of the task that cannot be improved, even as the efficiency of the optimized components increases. In short, Amdahl’s Law provides a theoretical limitation on the maximum performance gain achievable through parallelization or optimization in a computing system.


The phonetic pronunciation of Amdahl’s Law is: æm-dɑl(z) lɔ

Key Takeaways

  1. Amdahl’s Law provides a formula to determine the maximum improvement in a system’s performance due to parallelization or optimization of a particular component.
  2. It highlights the importance of addressing the slowest or least optimized components in a system, because the overall speedup of a system is limited by the time taken by the slowest component.
  3. Amdahl’s Law emphasizes that it becomes increasingly difficult to achieve significant performance improvements with parallelization, once a certain level of optimization has been reached, as the serial, non-optimizable portion of the system will become the performance bottleneck.

Importance of Amdahl’s Law

Amdahl’s Law is an essential principle in the field of computer architecture and parallel computing, as it provides a fundamental limit on the extent to which a computational task can be sped up by adding more processors.

Named after computer scientist Gene Amdahl, it suggests that a system’s overall performance improvement is bound by the fraction of its non-parallelizable portion, emphasizing the need for careful consideration of task parallelism during a system’s design.

This law highlights the diminishing returns of increasing parallelism, guiding engineers, and researchers to optimize multi-core architectures and software applications, ensuring efficient allocation of resources and effective usage of processing power.


Amdahl’s Law, proposed by Gene Amdahl in 1967, serves as a valuable tool to predict the maximum improvement achievable in a computing system when only a portion of it is enhanced. Its primary purpose is to provide a comprehensive understanding of the performance limitations in any optimization effort as well as to highlight the importance of addressing the bottlenecks in a computing process. The law assists in evaluating the potential benefits of incorporating parallel processing or improving specific parts of a system.

By assessing this performance improvement, system designers and engineers can make well-informed decisions on allocating resources and improving the specific parts of an infrastructure, providing optimal enhancements to the overall system’s functionality. In practical terms, Amdahl’s Law allows IT professionals to concentrate on the system’s most time-consuming elements to achieve the most significant enhancements. The law emphasizes how focusing on the system’s slowest section yields the best possible outcome in terms of performance.

Furthermore, it suggests that there is diminishing return on investment in improving a particular subsystem beyond a certain point. Amdahl’s Law also helps researchers and developers recognize the importance of creating scalable solutions that can efficiently leverage multiple processing units to achieve optimal results in an increasingly parallel computing environment. Overall, Amdahl’s Law plays an essential role in understanding, evaluating, and optimizing computing performance, helping designers and engineers to develop efficient systems that can meet ever-evolving technological requirements.

Examples of Amdahl’s Law

Amdahl’s Law is a principle that states the maximum speedup achievable for a computing task by improving a specific subsystem or portion of the task. It is commonly used to estimate the overall performance improvement of a computing system when one of its parts is upgraded or optimized. Here are three real-world examples of Amdahl’s Law in action:

Parallel Computing:Parallel computing involves executing tasks concurrently on multiple processors, with the aim of speeding up computation. Amdahl’s Law can be applied to estimate the maximum speedup that could be achieved by dividing the task into smaller, parallelizable subtasks. In this context, Amdahl’s Law helps to determine how much of a performance boost can be gained with a given number of processors.For example, if 60% of a program can be parallelized, and the remaining 40% must remain sequential, Amdahl’s Law would show that even with an infinite number of processors, the maximum achievable speedup is only

5 times that of the original program.

Graphics Processing:Modern GPUs (Graphics Processing Units) have been designed to perform data-parallel operations simultaneously across hundreds or thousands of threads. Amdahl’s Law can be applied in the context of optimizing graphics performance for gaming or multimedia applications.For instance, consider a video game that relies on both a CPU and a GPU for rendering graphics, with 80% of the rendering tasks being offloaded to the GPU. If only the GPU is upgraded to a significantly more powerful version, the maximum achievable speedup would be limited by the 20% of the workload handled by the CPU.

Cloud Computing:Amdahl’s Law is also applicable in cloud computing, where multiple virtual machines or instances are used to distribute computing tasks. By applying Amdahl’s Law, system architects and developers can estimate the maximum speedup that can be achieved by increasing the number of instances and optimizing the workload distribution.For example, a cloud-based web application might have 70% of its tasks distributed across several instances, while 30% of the work is still centralized on a single instance. In this case, Amdahl’s Law can help determine the diminishing returns gained by adding more instances to tackle that 70% of parallel tasks since the 30% portion remains a bottleneck.


Amdahl’s Law FAQ

What is Amdahl’s Law?

Amdahl’s Law is a principle that describes the performance improvement of a computing system when a portion of the system is enhanced. It was first defined by Gene Amdahl in 1967 and helps designers understand the limitations and potential benefits of parallel processing and system upgrades.

How is Amdahl’s Law represented mathematically?

Amdahl’s Law can be represented mathematically as follows: S = 1 / [(1 – P) + (P / N)], where S is the speedup of the system, P represents the proportion of the program that can be parallelized, and N represents the number of processors or computing resources used.

What are the key takeaways from Amdahl’s Law?

The key takeaways from Amdahl’s Law are that parallelization can greatly improve the performance of a system, but there is a limit to these improvements due to the sequential portion of a program, and that increasing the number of processors may not always lead to significant performance improvements, especially if the parallelizable portion is small.

What are the factors that affect Amdahl’s Law?

There are three key factors that affect Amdahl’s Law: the proportion of the program that can be parallelized (P), the number of processors or computing resources used (N), and the efficiency of the parallelized portion’s execution.

How can Amdahl’s Law be used to make decisions about system upgrades?

Amdahl’s Law can be used to evaluate the potential impact of system upgrades on performance. By estimating the values of P, N, and other relevant parameters, system designers can make informed decisions about the cost-benefit analysis of investing in additional parallel processing resources or other upgrades.


Related Technology Terms

  • Parallel Computing
  • Speedup
  • Scalability
  • Concurrency
  • Processor Performance

Sources for More Information

  • Wikipedia (
  • GeeksforGeeks (
  • ScienceDirect (
  • Baeldung (

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