A handful of command line switches are processed by the VM and not the library. They control low-level features.
-i=imageSpecifies the image file to use; see Images
-datastack=nDatastack size, kilobytes
-retainstack=nRetainstack size, kilobytes
-callstack=nCallstack size, kilobytes
-callbacks=nCallback heap size, kilobytes
-young=nSize of youngest generation (0), megabytes
-aging=nSize of aging generation (1), megabytes
-tenured=nSize of oldest generation (2), megabytes
-codeheap=nCode heap size, megabytes
-pic=nMaximum inline cache size. Setting of 0 disables inline caching, >= 1 enables polymorphic inline caching
-fepenter low-level debbugger, aka fep mode immediately
-no-signalsturn off OS signal handling
-consoleopen console if possible

If an -i= switch is not present, the default image file is used, which is usually a file named factor.image in the same directory as the Factor executable.