You can reconfigure the amount of memory allocated to a virtual machine to enhance performance.

About this task

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 compatibility setting.

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 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.

The memory size must be a multiple of 4MB.

Table 1. Maximum Virtual Machine Memory

Introduced in Host Version

Virtual Machine Compatibility

Maximum Memory Size

ESXi 5.5

ESXi 5.5 and later


ESXi 5.1

ESXi 5.1 and later


ESXi 5.0

ESXi 5.0 and later


ESX/ESXi 4.x

ESX/ESXi 4.0 and later


ESX/ESXi 3.x

ESX/ESXi 3.5 and later


The ESXi host version indicates when support began for the increased memory size. For example, the memory size of a virtual machine with ESX/ESXi 3.5 and later compatibility running on ESXi 5.0 is restricted to 65,532MB.


Power off the virtual machine.

Verify that you have the Virtual machine > Configuration > Memory privilege on the virtual machine.


  1. Click Virtual Machines in the VMware Host Client inventory.
  2. Right-click a virtual machine in the list and select Edit settings from the pop-up menu.
  3. On the Virtual Hardware tab, expand Memory.
  4. In the RAM text box, type the amount of RAM to assign to the virtual machine or select one of the suggested values from the drop-down menu.
  5. Select whether the memory is specified in MB or GB.
  6. Click Save.