There wasn't just one. Some defrag tools from the days of DOS would actually let you pick. A commonly used one was to try to place the contents of the same dire

There wasn't just one. Some defrag tools from the days of DOS would actually let you pick. A commonly used one was to try to place the contents of the same directory adjacent to each other on the disk surface, to minimize latency. I can't remember which it is, but either the center or the outside edge of a disk read faster, so another common trick was to place all the files necessary to boot the system there, to reduce boot times.