Virtual memory refers to the memory available for virtual machines from the physical memory present on the host. VMkernel makes the operating system in a virtual machine take the virtual memory and use it as a physical memory for all its operations. Virtual memory is not limited to the size of the physical memory available, and can be extended or limited as per requirements of the virtual machine.
vSphere offers flexible memory management solutions and different kind of memories as per different needs. Three different memories used by vSphere are:
Host physical memory: The memory which is physically present on the host. This memory is managed by VMkernel and provides addressable memory space to the virtual machine.
Guest operating system physical memory: The memory which is presented to the virtual machine once it is created.
Guest operating system virtual memory: The memory which is presented to the application by the guest operating system.