Today, IT organizations have encountered growing challenges in the management and maintenance of large scale heterogeneous distributed computing systems because these systems have to be active and available at all hours. Therefore, it is difficult for administrators to manage such systems and handle changes occured at all hours. Moreover, current programming languages, methods, and management tools are inadequate to handle complexity, heterogeneity, scale, dynamism, and uncertainty as the most important challenges in such systems. Therefore, researchers investigate new ideas to address the problems created by IT complexity. One such idea is Autonomic Computing (AC). Autonomic Computing Systems (ACSs) are systems that manage themselves. This paper provides a thorough survey of autonomic computing systems, presenting their definitions, their characteristics and effects on quality factors, their architecture, issues and challenges.