first_unused_memory and thread creation

I'm interested in knowing what the 'first_unused_memory' request value is referring to upon program creation.  The value always seems to point the the same place, no matter how many threads I pre-define.  Also, with calls such as 'ux_system_initialize' which requires a large chunk (~131K) of memory to be provided to it I would think doing a malloc, instead of providing the current pointer as obtained from the 'first_unused_memory' value upon start.  All examples seem to use this value and increment as used.

Thanks,

Rich