"The MicroSD card is formated as a FAT32 partition." eMMC is formated as a FAT32. MicroSD is of course what ever user puts there.
The Nokia N900 has a 32 GB eMMC, 256 MB NAND internal storage and a hot swappable microSD card slot which support up to 16 GB of additional storage (this number is based on what was available for certification and may not reflect the actual capacity support of the device). The 32 GB is formated as 768 MB of swap, ~1 GB of ext3 mounted on /home (for extra applications) and ~25 GB of FAT32 mounted on /home/user/MyDocs (for movies, music, documents).[5] The 256 MB NAND contains the bootloader, kernel and rootfs.