Measurements of an interactive computer system at Piper's...

Measurements of an interactive computer system at Piper's Pickles show that the average response time is 1.5 seconds, the number of active users is 100 , the CPU utilization is $75 \%$, and the average CPU time used per interaction was 0.3 seconds. What was the average think time?

Key Concepts

Service Demand

Service demand refers to the average amount of processing time (e.g., CPU time) required to handle a single interaction. It is a key measure used to characterize the workload imposed on the system by each user interaction.

CPU Utilization

This is the proportion of time the CPU is actively processing tasks. In performance evaluation, CPU utilization is used together with service demand and throughput to determine system performance and potential bottlenecks.

Closed-System Throughput and Little's Law

In closed-loop performance models, the relationship between the number of users, their interaction times (response time plus think time), and system throughput is formalized by Little's Law. This law states that the number of users equals the product of throughput and the cycle time (the sum of response time and think time), making it a powerful tool for analyzing interactive systems.

Response Time

This is the total time a system takes to process a request from the moment it is made until the response is received. It includes the service time as well as any additional delays due to system overhead or queuing effects.

Think Time

In interactive system analysis, think time is the duration a user spends between receiving a response and issuing the next request. It represents the delay external to the system processing and is crucial for understanding overall system throughput and user experience.

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