The 3 approaches in Computer Performance Evaluation

1. Benchmarking: The system can be built then modified and finally measured

+ "performance estimate is perfectly accurate"
+ it is based on a real system so it is sure that there haven't been introduced any errors that are not in the real system.

- high cost
- not flexible
- time consuming

2. Simulation: to build a simulation model of the system, which can be validated against the already existing system. After the validation several needed modifications can be derived.

This approach permits an arbitrary level of detail to be included:
+ any system feature can be included and checked
- there is the danger to include too many features(which are not so essential for the performance of the required system) of the real system to the simulation increasing complexity and cost

3. Analytic Modeling: to construct a mathematical model (via a combination of algorithmic and numerical procedures) of the system and then perform validation, as in simulation.

+ The model is constructed faster
+ The solution is calculated faster than in simulation or benchmarking for the final system
+ it provides a significant estimation of the behavior of the potential system without first implementing it. Thus it is a much cheaper technique.