Question about HP 41CX Memory Allocation

[EdFab]

I believe I have a fully functional HP 41CX but there is something I don't understand about memory allocation. I've been reading the online instruction manual for the HP 41C, and it says that the SIZE function will prompt for a 3-digit number between 000 & 318. Since the HP 41C comes with 63 registers, I'm assuming that the 318 limit only realistically applies if extended memory modules are installed. Please correct me if I'm wrong about this assumption.

After doing a memory clear on my HP 41CX, I did a shift->GTO .., and got "00 REG 219" in the display. I interpret this to mean that there are 100 data storage registers allocated, with 219 registers available for programming.

However, I have an X Memory module installed (I believe it's a double X Memory module at that, since CATALOG 4 gives me 600 in the display).

So my question is: Is it possible to allocate some of the registers on the X Memory module for data allocation? Could I enter SIZE 400 for example? (I'm guessing I can't based on the display of 00 REG 219 mentioned earlier when I pressed GTO .. with the X memory module installed).

Incidentally, I get the display of 00 REG 219 whether the X Memory is installed or not. So how does the X Memory module come into play at all?

I'm pretty clueless about this, I admit.