HP PRIME - Available Memory / Memory in use ...

[debrouxl]

The Prime's OS is loaded from the 256 MB NAND Flash memory to the 32 MB RAM during the booting stage, and runs from RAM, using at least half of it. That's because NAND Flash memory can be accessed exclusively in paging mode, and it's therefore unsuitable for code execution.
There's another type of Flash memory: NOR Flash memory, which is random access and therefore eXecutable In Place, but is usually fairly slow, and most of all, (much) more expensive than NAND Flash memory for a given capacity.
The high-end models from both HP (Prime) and TI (Nspire) use NAND Flash memory; calculator families based on older technology, e.g. the Flash-equipped subset of the TI-Z80, TI-68k and TI-eZ80 series, use XIP NOR Flash memory chips.