depth-first search
A search order on a tree (or dag) that searches each possibility as deeply as possible, exploring all options, before moving on to the next possibility. The alternative.
disk filing system
The first filing system on the BBC microcomputer that supported single density floppy diskettes (100K single sided, 200K double sided, considered 2 separate drives, or twice as much with an 80 track drive) using the 8271 controller chip. It supported only a single-letter (unnested) directory structure; however, this was generally good enough for such a small diskette.