GnuStep Runtime vs. et. al.

[Joe Graham]

Hello,
Could someone please explain the _runtime_ differences of Gnustep, Darwin
ObjC runtime and POC?  Actually the POC runtime is pretty well documented so
it is fairly clear about the POC object model however there is no expansion
(to my limited knowledge) of gc or dynamic linking.  Any information on this
would be helpful as I am pretty clueless to the whole subject matter.  I
would just like to know persay, "what am i giving up?" if I tried to build
an application with GNUstep Launch Pad? (say for example a console app)  It
seems obvious that the goal would be to have one runtime and compilation
strategy across multiple platforms with minimum porting effort.  However it
would also be interesting to know that you could simply take one codebase
and port it across runtimes?  Also does anyone know the portability of the
Darwin runtime?  I have posted this on the comp.lang.objectivec and was
pretty much ignored.  (*sigh*)  Anyone know where I can find the technical
details of compilation / runtimes of Objective C implementations?

-joe