Modify the shared heap buffer sizes

If you reduce the size of the common or interactive memory, you leave more memory available for non-interactive desktops. However, reducing the sizes of either of these might cause performance problems. Microsoft® sets these values by default because their tests show that these are the required values. You are not recommended to change these values.

Reducing the memory used for a non-interactive desktop will allow more desktops to be created. Individual processes that require more memory might be impacted, but most processes will run successfully. If your default non-interactive desktop memory (third entry) is 512, try reducing it to 256. See Modify the Windows registry entries that determine the heap size for how to do it.