There are times when you need to save the current state of an application's or operating system's configuration before you experiment with a change. A real-life example would be during a system development life cycle where changes are inevitable, and you need the ability to undo a change. vSphere allows you to save the state of a virtual machine regardless of its power state.
A virtual machine snapshot can capture the following data:
The virtual machine's memory contents
The virtual machine's settings
The state of the virtual disks
For you to perform snapshot operations on a virtual machine, you need to be connected to the vCenter Server either by using vSphere Web Client or vSphere Client, or by using the vSphere Client to the ESXi server hosting the virtual machine.