After version 4.1 (released in 2010), VMware renamed ESX to ESXi.
ESXi replaces Service Console (a rudimentary operating system) with a more closely integrated OS.
Virtual machines are no different than physical computers and normally sync time using the same domain hierarchy.
Lately, however, I've seen VMs running on VMware v Sphere boot up with random time differences from the domain.
For ESXi versions 4.0, 4.1, 5.0, 5.1 and 5.5, VMware highly recommends you to update ESXi hosts to ESXi 5.5 Update 3b while managing them from v Center Server 5.5 Update 3b.
Virtual Disk Development Kit (VDDK) 5.5.3 adds support for ESXi 5.5 Update 3 and v Center Server 5.5 Update 3 releases. Virtual SAN does not support clusters that are configured with ESXi hosts earlier than 5.5 Update 1.
Normally, time is synchronized in a Windows domain using the domain hierarchy.
At normal run-time, the vmkernel is running on the bare computer, and the Linux-based service console runs as the first virtual machine.
VMware dropped development of ESX at version 4.1, and now uses ESXi, which does not include a Linux kernel.
Note: If you are using a legacy virtual machine - a virtual machine created under VMware Workstation 3 and not upgraded to use the new VMware Workstation 4 virtual hardware - you must power off the virtual machine before taking a snapshot.
For information on upgrading the virtual hardware, see Upgrading VMware Workstation.