Simplest (practical) file system

The biggest problem that I see here is that Bob wants to be able to use this OS on systems that have as little as 16k words but still use LARGE modern drives. -- I have been thinking about this a LOT lately relating to using older CPUs with few or none of the original peripherals, and it may make sense, since you're building an IDE interface anyway, to build a file level interface onto the card, rather than talking to the drive as an unstructured block device. The idea I've been toying with is building an interface card like this with a local processor, disc, ethernet, etc. and using it in conjuction with a remote system that would provide the console / debugging UI / shared peripherals for a bunch of different processors that I have. This would also reduce the in-core footprint of the OS, since the file system (and networking in my case) is handled on the interface card.