The following info has been on Wikipedia for ages, so, it wasn't unexpected at all:

The Nokia N900 has 32 GB eMMC and 256 MB NAND non-removable storage.[2] Additional storage is available via a hot swappable microSDHC card socket, which is certified to support up to 16 GB of additional storage.[46] The microSDHC card can be formatted with a supported file system such as ext2, ext3, FAT16 and FAT32.[citation needed]

The 32 GB eMMC is split into 3 partitions [47]:

* 2GB as ext3 mounted to /home
* 768MiB as swap
* the remainder as VFAT mounted to /home/user/MyDocs with about 25GB of free space.

The 256 MB NAND is formatted as UBIFS[48] and contains the bootloader, kernel and root directory "/"[citation needed] with about 100MB of free space.[49]

Programs larger than 500KB including dependencies should be stored in /opt which is symlinked to /home/opt and therefore located on the 2GB ext3 partition. The VFAT partition is also available for storage but needs to be used carefully as it is unmounted and exported if a usb cable is connected to the device.[49][50]