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With this hypervisor feature, the sum of the memory allocated to VMs on a host can exceed the amount of physical memory on that host. While this seems counterintuitive, the theory behind memory overcommitment is that every VM on a host won't use all of its allocated memory at any given time. When one VM has excess memory, its unused memory is available for other VMs to use. For example, a host server with 16 GB of memory might be able to run five VMs, each allocated with 4 GB of memory. VMware ESXi checks memory use every 60 seconds and automatically reallocates unused memory, which makes managing the environment easier for virtualization administrators and allows for higher VM density than other memory management techniques. With VMware ESXi, you can take advantage of this feature no matter what OS you're using. Hypervisor type aside, memory overcommitment allows for better resource utilization and further optimizes the environment.