Why does the RAM value change upon resuming a suspended Windows virtual machine?

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When running your Windows virtual machine (VM), you may notice that the amount of RAM used up is inconsistent with what you have allocated. For instance, you may have assigned 8 GB of RAM to the Windows VM and suspended it. Upon resuming you may see that the amount of RAM used up by the VM is actually lower than 8GB that you can see in Activity Monitor.


In two words - it's expected. Let's dive deeper into the details:

Whenever the Windows virtual machine is booted, Windows assigns all available physical memory allocated to the VM by filling it with zeroes. This action marks all the memory assigned to the virtual machine as used.

When you suspend the virtual machine, the empty memory pages (filled with zeroes) are not saved in the state.

When you resume the virtual machine, the empty pages are not restored, causing the memory pages that were marked as used before the pause to appear free. This can make it seem like there's a difference in memory usage, but in reality, there's no actual change in the amount of memory being used.

The virtual machine RAM usage should stabilize after the booting process is completed, and the actual memory usage should be displayed in Activity Monitor.

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