**Author details**

12 Will-be-set-by-IN-TECH

Processor and memory utilization (1-1-3)

0 2 4 6 8 10

0 2 4 6 8 10

**Figure 13.** Processor (-o-) and memory (-x-) utilization for a 2-1 processor; *lt* = 10, *tm* = 5, *tcs* = 3,

Simultaneous multithreading discussed in this paper is used to increase the performance of processors by tolerating long–latency operations. Since the long–latency operations are playing increasingly important role in modern computer system, so is simultaneous multithreading. Its implementation as well as the required hardware resources are much simpler than in the case of out–of–order approach, and the resulting speedup scales well with the number of simultaneous threads. The main challenge of simultaneous multithreading is to balance the system by maintaining the right relationship between the number of simultaneous

All presented results indicate that the number of available threads, required for improved performance of the processor, is quite small, and is typically greater by 2 or 3 threads than the number of simultaneous threads. The results show that a larger number of available threads

number of available threads

**Figure 12.** Processor (-o-) and memory (-x-) utilization for a 1-1 processor; *lt* = 10, *tm* = 5, *tcs* = 3,

number of available threads

Processor and memory utilization (2-1-3)

0

0

threads and the performance of the memory hierarchy.

provides rather insignificant improvements of system's performance.

0.2

0.4

0.6

utilization

0.8

1

0.2

0.4

0.6

utilization

*ps*<sup>1</sup> = 0.2, *ps*<sup>2</sup> = 0.1

*ps*<sup>1</sup> = 0.2, *ps*<sup>2</sup> = 0.1

**5. Concluding remarks**

0.8

1

Wlodek M. Zuberek *Memorial University, St.John's, Canada, University of Life Sciences, Warsaw, Poland*

#### **6. References**

[1] Patterson, D.A., Hennessy, J.L. (2006). *Computer architecture – a quantitative approach* (4-th ed.); Morgan Kaufmann.

**A Petri Net-Based Approach to the Quantification**

**Chapter 14**

Data center availability and reliability have accomplished greater concern due to increased dependence on Internet services (e.g., Cloud computing paradigm, social networks and e-commerce). For companies that heavily depend on the Internet for their operations, service outages can be very expensive, easily running into millions of dollars per hour [15]. A widely used design principle in fault-tolerance is to introduce redundancy to enhance availability. However, since redundancy leads to additional use of resources and energy, it is expected to

Data center designers need to verify several trade-offs and select the feasible solution considering dependability metrics. In this context, formal models (e.g., Stochastic Petri nets and Reliability Block Diagrams) are important to provide estimates before implementing the data center system. Additionally, a growing concern of data center designers is related to the identification of components that may cause system failure as well as systems parts that must

In this work, we propose a set of formal models for quantifying dependability metrics for data center power infrastructures. The adopted approach takes into account a hybrid modeling technique that considers the advantages of both stochastic Petri nets (SPN) [22] and reliability block diagrams (RBD) [10] to evaluate system dependability. An integrated environment, namely, ASTRO [20] has been developed as one of the results of this work to automate

This section briefly touches some fundamental concepts as a basis for a better understanding

©2012 Callou et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0),which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly

©2012 Callou et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**of Data Center Dependability**

Additional information is available at the end of the chapter

João Ferreira and Rafael Souza

http://dx.doi.org/10.5772/47829

**1. Introduction**

**2. Preliminaries**

of this work.

Gustavo Callou, Paulo Maciel, Dietmar Tutsch, Julian Araújo,

have a negative impact on sustainability and the associated cost.

be improved before implementing the architecture.

dependability evaluation of data center architectures.

cited.

