HP50g ram and working dir.

[Claudio L.]

(08-16-2017 01:55 PM)pier4r Wrote:  So I was reading the interesting thread about FRAM cards (nice piece of technology).

Then I realized that in the hp50g port0 is the HOME directory, but there is another ram port, port1 (IRAM 127Kb).

As far as I know, with firmware 2.15, if one does some computation, the memory in port 0 is used. Would it be possible to have, as working ram directory, port1 ? So one can mess around there, then move the results either in home/port2 (I find port3 mostly usable for backups at the moment, still very valuable).

The old Saturn processor had only 20 bits addresses, and it counted in nibbles, not bytes so it could only address 2^19 = 512 kbytes of memory. Part of that address space was taken by the ROM, leaving only 256 kbytes maximum RAM addressable directly. Anything beyond that has to be temporarily mapped in banks (these are the ports).
So the extra RAM was assigned to Port1 because the 50g already maxed out the addressing capacity of the Saturn, it can't be used directly for directories and variables because is not contiguous to the main memory, and has to be mapped in/out all the time, but you are free to STO/RCL/PURGE objects in it. You are not allowed to create a directory structure in port memory, though, all your variables will be at the root so is not the best choice for organization.