Calvin,

Excuse me for jumping in here, but I happened to come across this thread and got interested.

I would add to Vlad's response that when A is derived from B, A and B are both in memory, but A's contents are much smaller then B's because A contains a reference to B and instructions on what changes were made in B to produce A.

When you instantiate A and test for memmory used, the derive A from B, the amount of memory used is much less than double. Clearly then A is referencing B for a lot of the information used to create A.

What that tells me is that if I create B then derive one instance from it, I have actually used up more memory than if I just used B instead of deriving A from it and using A. But if I derive A, C, D, E, and F., the memory savings are considerable over using B five times.

regards,