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Transactional Memory is currently being advocated as a promising alternative to lock-based synchronization because it simplifies multithreaded programming. In this way, future many-core CMP architectures may need to provide hardware support for transactional memory. On the other hand, power dissipation constitutes a first class consideration in multicore processor design. In this work, we characterize the performance and energy consumption of two well-known Hardware Transactional Memory systems that employ opposite policies for data versioning and conflict management. More specifically, we compare the Log TM-SE Eager-Eager system and a version of the Scalable TCC Lazy-Lazy system that enables parallel commits. To the best of our knowledge, this is the first characterization in terms of energy consumption of hardware transactional memory systems. To do that, we extended the GEMS simulator to estimate the energy consumed in the on-chip caches according to CACTI, and used the interconnection network energy model given by Orion 2. Results show that the energy consumption of the Eager-Eager system is 60% higher on average than in the Lazy-Lazy case, whereas performance differences between the two systems are 42% on average. Finally, we found that although on average Lazy-Lazy beats Eager-Eager there are considerable deviations in performance depending on the particular characteristics of each application.