Using a laptop with 4GB of RAM, trying to install ESX 4.0 Update 1. Allocated 2GB RAM to the virtual machine but receiving the following error when trying to power it on:

Not enough physical memory is available to power on this virtual machine with its configured settings.
To fix this problem, decrease the memory size of this virtual machine to XXXXMB, or adjust the additional memory settings to allow more virtual machine memory to be swapped.
Alternatively, do you want to temporarily reduce the memory size of the virtual machine from 2048MB to XXXXMB? Reduce Memort | Do Nothing

The only option of any use is of course “Do Nothing”. ESX 4.0 won’t install without a minimum of 2GB of memory.

To fix the issue and allow the virtual machine to power on with its allocation of 2GB memory: In Workstation, go to Edit -> Preferences -> Memory tab then increase the Reserved Memory slider up to the desired amount of memory. I increased it to exactly 2048MB and the ESX 4.0 virtual machine could be powered on.

Also tested with lower values and it will also work – it depends on the Additional Memory setting. The default option is to ‘Allow some virtual machine memory to be swapped’ (switching to the ‘Fit all virtual machine memory into reserved host RAM’ option, will result in the VM failing to power on if the Reserved Memory allocation is lower than the amount of memory allocated to the virtual machine).