HP 50G help

[Claudio L.]

(08-14-2015 04:25 PM)Hlib Wrote:  Anybody, please, describe to me properties of a port 0:IREM. What does it necessary for? My experience doesn't coincide with the description in AUR and UG (HP-50G). It is like hidden-reserved scope.

The "Ports" are areas of memory for storage, typically used for data that is not modified often.
To fully understand "why" there's port memory when you could perfectly well store things in variables you need to look back in time. Back in the day you had a small amount of ram, and you could buy memory cards to "expand" your memory.
Originally, the numbered Ports were those additional RAM modules you could install in an external RAM card. Some cards would allow to "merge" part of that extra RAM into your main memory, and the rest was in "Ports".
Access to those ports was in "banks", so not all memory was visible at all times, you had to switch banks to access the different ports.

Now as far as Port 0: it's in main RAM, takes your user space, and is not banked, so it's actually none of the above. But it retains that special way to access it, separate from the rest of the memory.
Port 0 actually grows and shrinks as you store objects, so it's slow to store objects (it's much faster to store them in variables). However, because it's not banked, reading from it is very fast, unlike for instance Port2, which is banked and it's Flash, not RAM.
I personally have never, ever used Port0 for anything, as it consumes main RAM permanently. On the 50G you have Port1 (ERAM) for that, which is banked (hence a bit slower access) but doesn't consume main memory. And for more permanent libraries, port 2 (Flash).
There's, however, some old libraries that may need to run from Port0 because they are incompatible with banking. They are very rare but you may find some in hpcalc.org (the installation instructions would tell you if you must install in Port0).
That's the only "modern" use I can think of for Port 0.