The levels of immersion and presence felt by users in a Virtual Environment (VE) are very important factors that dictate the quality of the Virtual Reality (VR) experience. Sensori-motor systems, both hardware and software, are the components of a VR system that contribute to generate the VEs and to create the feeling of being there. This paper reviews the different visualization hardware/software components that are at the heart of a VR system and provides means for assessing their performance in the context of various applications. Because of its historical and functional importance in the field of VR, visualization hardware is reviewed first (HMDs, VRDs, stereo glasses, CRT, LCD monitors and Plasma displays...). Then, a list of the most important insights, which should be addressed when designing and assembling a VR system, are discussed. Finally, visualization software is covered in the context of the available hardware components.