Embedded devices need storage that takes little power and is physically compact, robust, and reliable over a lifetime of perhaps tens of years. In almost all cases, this means solid-state storage. Solid-state storage was introduced many years ago with read-only memory (ROM), but for the past 20 years, it has been flash memory of some kind. There have been several generations of flash memory in that time, progressing from NOR to NAND to managed flash such as eMMC.
NOR flash is expensive but reliable and can be mapped into the CPU address space, which allows you to execute code directly from flash. NOR flash chips are low capacity, ranging from a few megabytes to a gigabyte or so.
NAND flash memory is much cheaper than NOR and is available in higher capacities, in the range of tens of megabytes to tens of gigabytes. However, it needs a lot of hardware and software...
