FT can work internally with an editing resolution of up to 8190 samples. It can alternatively work with an external binary file of up to about 1GB as the source of the terrain altitude (that's about 30000x15000 for a 16-bit data element). FT doesn't need to load the entire planet at once. It's possible to load a smaller area as a height field and just work with that (for example, a local GTOPO30 section or a USGS DEM). The biggest limitation is that FT is a 32-bit program and wants to keep everything mapped into memory. On a 64-bit OS, it should be able to get almost 4GB of workspace for everything (program code, housekeeping data, editing data, undo space, binary files mapped into memory, and so on); for a 32-bit OS version, everything would need to get crammed into 2GB of space. Back in 1999 when FT was being developed, 2GB was a huge amount of space; it's a bit less so these 15 years on...