We only support Windows NT derivatives now.

Doc/library/msvcrt.rst

@@ -153,6 +153,4 @@ Other Functions
 .. function:: heapmin()
 
    Force the :cfunc:`malloc` heap to clean itself up and return unused blocks to
-   the operating system.  This only works on Windows NT.  On failure, this raises
-   :exc:`IOError`.
-
+   the operating system.  On failure, this raises :exc:`IOError`.

PC/msvcrtmodule.c

@@ -47,8 +47,7 @@ PyDoc_STRVAR(heapmin_doc,
 "heapmin() -> None\n\
 \n\
 Force the malloc() heap to clean itself up and return unused blocks\n\
-to the operating system. This only works on Windows NT. On failure,\n\
-this raises IOError.");
+to the operating system. On failure, this raises IOError.");
 
 // Perform locking operations on a C runtime file descriptor.
 static PyObject *