When a firm purchases computing power from a central computing service and pays only for the amount of computing power it uses, this is commonly referred to as:

The concept described in the question is utility computing, which refers to a model where firms can buy computing power as a service from a central provider and are charged based on their usage. This operational model is akin to how utilities like electricity or water are billed: customers pay only for what they consume, allowing for flexibility and scalability.

In utility computing, organizations can scale their resources up or down according to their current needs without the need for substantial upfront investment in hardware or infrastructure. This approach is particularly beneficial for businesses looking to manage costs effectively while ensuring that they have the computing resources necessary to support their operations.

Other options like grid computing, edge computing, and autonomic computing do not align with the described payment model based on usage:

• Grid computing refers to a distributed computing model where resources from multiple locations are used to work on a common task, typically to improve efficiency for large-scale computational tasks.

• Edge computing focuses on processing data closer to the location where it is generated, reducing latency and bandwidth use but does not inherently relate to cost based on usage.

• Autonomic computing refers to systems capable of self-management regarding configuration, healing, optimization, and protection, but does not deal directly with utility pricing models.

Thus, utility computing is the most appropriate