Periodically saving track to SDcard, append or overwrite?

Hi!
When the periodically saving track data to SDcard is enabled, is the track data appended to the SDcard file and deleted from RAM or is the track data kept in RAM and periodically overwriting the file on the SDcard?
My concern is the amount of data in the RAM; if kept it will keep on growing while tracking eventually fill up the memory (also, if using lots of RAM it is more likely to be killed by OS when other apps need to run), if moved/appended to SDcard file the RAM memory will never grow above some amount.


Best regards /Anders