Calculators that allow direct operations on data stored on persistent storage?

[pier4r]

Maybe the title is not so clear, I give some more info. After having written the wall of text below, I am not sure I clarified the problem :/ .

We know that physical calculators (or mobile systems in general) have little ram if one wants that the battery lasts long. Normally the ram is some kilobytes in size . 64kb for the casio 9860 and primz, 270kb for the 50g with userRPL, ~350kb + with the 50g with newRPL, some megabytes for ti nspire and hp prime, etc...

If one is doing some little data collection over the days, say 500bytes per day, the ram won't be enough after a while. Especially if one wants to pack the data collected in one object, say a list.
In this case I am ruling out the option that one is doing a workaround with partial lists that then have to be packed together somehow. In other words I am ruling out the option that the user himself is going to create an ad hoc solution to move "pages" of data between the ram and the persistent storage.

Therefore would be neat to have the possibility to modify directly the data while this is residing on the persistent memory (internal storage or external storage like SD cards), without the need to recall all the data in memory. That is, the operating system of the calculator (or a library) is going to work for the user to recall only part of the data, modify it, and put it back.

So far I know that only the newRPL allows this. Do you know any other OS or OS+libraries that allow to modify data stored on the persistent storage without recalling the entire data object in ram?
That is, allowing to create data objects that may be larger than the available ram (but obviously smaller than the available storage).

To make an example I mean the following.

I have a data object of 20kb. I add 1kb of data more, now it is 21kb.
To do the addition, instead of recalling the object in ram (occupying 20kb of ram) I recall only a fraction of it (using less ram than 20kb). At the end of the operation the data object on the persistent storage occupies 21kb containing the added content.

On the 50g with userRPL , whether I use port1 (ram), port2(flash) or port3 (sd card) I always need to recall first the entire object in ram, so I need to have enough ram free, work on it, and then save it again.

I have an object that is growing almost every day on the 50g. For the moment it is 21kb, and I need to have twice-three times its size of ram (port0) free for additional operations because I cannot edit directly the object saved on the persistent storage (at least not if I use the hp 2.15 firmware). For my predictions, unless I develop a paging solution, at the end of this year I may run out of ram.
Hence the question.

Sure one can say "use a prime that has megabytes of ram", but I'd like to know in general what is the status of the produced calculators and their software for data collection. (and at the end I will likely port the data on the newRPL OS)