vSphere Quick Boot is an innovation in conjunction with major server vendors that restarts the VMware ESXi™ hypervisor without rebooting the physical host, skipping time-consuming hardware initialization. Skipping Hardware initialization enables vSphere Quick Boot feature to perform faster software upgrades for ESXi. Refer to VMware KB 52477 for more details on this feature. Dell has been supporting Quick Boot from it's inception, the below documentation links provides specific Quick Boot support on different generations of Dell PowerEdge servers with various VMware vSphere versions.