Characteristic performance values

Every IT system can be divided hierarchically into the following levels:

• Application programs

  The user's requirements (as represented by the application programs) are transformed into tasks at the system software level, and into instructions and I/O operations at the hardware level.

• System software

  The system software no longer views the application programs as its workload, but rather the number of concurrent tasks and the differing demands they make.

• Hardware

  At hardware level the workload appears as a set of commands, input/output operations and storage reservations. At user level many different workloads can result in the same hardware workload.

The performance of an IT system is measured and evaluated with the help of characteristic performance values. This chapter examines the following aspects:

• Characteristic performance values of an online application

• Characteristic performance values of a batch application

• Formulating a performance expectation

• Relative performance factor of the CPU (RPF)

• Characteristic main memory values

• Characteristic peripheral values