ATA layers of progression as it relates to  media storage bios(dominated by  MSFT) addressing.  Every thing stems from....Hard Disk technology and having to be backward compatible through abstract layers.

Early HDD...CHS cylinder/ head/ sector(512 bytes) addressing....directly

Modern  HDD....CHS optionally converted to LBA or logical block addressing,  through an abstract layer. No problem for this conversion, as an HDD device does not have to be erased. However, there is a conversion process to keep the bios of MSFT compatible.

Then comes NOR flash,  a block device having LBA addressing (512byte)and needing to be compatible to a standard OS.  Where in,  you can not simply over right change like an HDD. In comes BAN with FTL,  translating the LBA of the flash back through CHS(512byte) bios to an OS.   This process was a combination managed through the physical cross point(parallel)properties of the flash as well as Ban's FTL.

Then comes NAND serial flash, still a block device(256byte) having LBA addressing and needing to be compatible to a standard OS. Yet, you can not leverage the physical makup, for it is not cross point,  it's serial or linear. This linear environment is not as easy to implement, if it's to support a robust utilization. For any type of abstract conversation of chs to lba....such as FTL, it would involve overhead.

In comes Norris/Daberko with their serially defined environment. This environment can be stand alone directly, or it can operate under the attributes of a legacy OS.  Where the abstract layers of the above are not necessary.

The  legacy OS in effect becomes the embedded OS through the API.

doni