HP-15C/DM-15CC Memory questions

[x34]

There are at least three versions of HP-15C ROM, supporting different memory models. The extended versions are called MEM80, MEM1B at David and Michael rpn-calc site.

What are the exact properties and limitations of these versions?
How to use extended registers and program steps, what does MEM show?

AFAIK, MEM80 is completely safe, and poses no risk at all.

[From Hong Kong]

Under the MEM1b version, the maximum memory is 896 bytes. This memory size is twice as much as that of the HP-15C.

Edited: 24 July 2012, 2:06 p.m.

[Jeroen Van Nieuwenhove]

See this thread.
Cheers,
Jeroen