Advancement in computer system hardware makes it difficult to meet the demands of teaching computer architecture and organization. Visualization of different architectures enhances the learning process among students by using simulators. Rather making a comprehensive simulator that can cater the requirement for the course, freely available simulators can serve the purpose as they can save time resource, ease of use, capacity to learn the concepts to fullest, can be accessed anywhere and anytime by the students. Finding the appropriate simulator for the course is a difficult task. This paper discusses about the simulators that can be used for the course Computer Architecture and Organization which can help instructors in making students able to grasp the knowledge delivered in lectures.