1. In a computing environment, a method of simulating a computing system, the method comprising a computer system performing the following: referencing a first data structure defining an application model to model a computer application, wherein the application model comprises: service models defined within the application model, the services models being designed to model application modules that process requests to implement functionality of the computer application, the definition of service models comprising definitions of hardware actions, wherein the service models are defined independent of definitions of hardware device models, wherein the hardware actions include: a number of cycles for a cpu; various sizes and types for Input/Output for a hard disk drive, the types specifying at least one of: a sequential read; a random read; a sequential write; or a random write, and an amount of network traffic; referencing one or more second data structures defining hardware device models, the hardware device models including definitions of computer hardware characteristics, including: a hard disk drive model defining a modeled latency for simulating and defining the hard disk latency according to I/O size, the model including: a property defining a constant for random reads; a property defining a slope for random reads; a property defining a constant for sequential reads; a property defining a slope for sequential reads; a property defining a constant for random writes; a property defining a slope for random writes; a property defining a constant for sequential writes; and a property defining a slope for sequential reads; such that a modeled hard disk latency can be calculated given the type of I/O operation and using a constant, an associated slope, and I/O size; latency for a cpu; and bandwidth for a network hardware model; referencing a performance scenario defining interconnections between the hardware device models and defining where the service models are applied to the hardware device models; and simulating the computer application in a hardware environment defined by the performance scenario.