The rapid growths in demand for computing resources and shift to Cloud Computing (CC) paradigm have necessitated the establishment of Virtualized Data Centers (DCs) known as Server Farms. In these centers, computing resources are virtualized, which consequently consume enormous electrical energy. This theoretical review presents background information and assess topic in a state of flux relating to energy-saving criteria in DCs using Ant Colony System (ACS) algorithms. The purpose is to avail its readership both early and mid- career researchers in computer discipline; critical literature review, existing research gaps and comprehensive bibliography as reference materials. Also, a literature review on other energy reduction using greedy approaches is included. Furthermore, sources of this review, research tools used by previous authors, adopted energy-saving strategies, taxonomy of ACS variants and reputable World’s publishers were analyzed. These are expected to pave way for the laying foundation in future research works.

Keywords : Cloud Computing, Virtualization, Virtualized Data Centers, Virtual Machine Consolidation/Placement, Ant Colony System.