You can reconfigure the memory allocated to a virtual machine's hardware.

Minimum memory size is 4MB for virtual machines that use BIOS firmware. Virtual machines that use EFI firmware require at least 96MB of RAM or they cannot power on.

Maximum memory size for a virtual machine depends on the host's physical memory and the virtual machine's hardware version.

If the virtual machine memory is greater than the host memory size, swapping occurs, which can have a severe effect on virtual machine performance. The memory size must be a multiple of 4MB. The maximum for best performance represents the threshold above which the host’s physical memory is insufficient to run the virtual machine at full speed. This value fluctuates as conditions on the host change, for example, as virtual machines are powered on or off.

Maximum Virtual Machine Memory

Introduced in Host Version

Virtual Machine Version

Maximum Memory Size

ESXi 5.0



ESX/ESXi 4.x



ESX/ESXi 3.x



The ESXi host version indicates when support began for the increased memory size. For example, the memory size of a version 4 virtual machine running on ESXi 5.0 is restricted to 65,532MB.


In the vSphere Client inventory, right-click the virtual machine and select Edit Settings.


Click the Hardware tab and select Memory.


Adjust the amount of memory allocated to the virtual machine.


Click OK to save your changes.