Easy Data Transform keeps all the data in memory for maximum performance. You can track the current memory usage in the Status bar.
Set Maximum memory usage in Preferences to the maximum amount of memory you want the Easy Data Transform process to use. If this is exceeded, you will be asked if you want to allocate more memory. It is generally not recommended to set this to more than the system RAM, otherwise Easy Data Transform will start using virtual memory (paging between RAM and disk) which is slow. The operating system can also crash or freeze if all the available virtual memory is used.
If Optimize processing for is set to Minimum memory use in Preferences then memory compression techniques are used to try to reduce the amount of memory required. This is generally recommended, as not using memory compression may use up all the RAM available and start using virtual memory to page between RAM and disk, which is likely to be a lot slower than the compression overhead.