[jrg]

As a side note, it has always been possible (on UFS at least) to link directories. It just gets a bit messy at fsck time, and older shells get a bit confused with 'cd ..'

Apple's implementation could have avoided linking directories - by creating new directories each time but always linking the files inside them - though I suspect that they decided it would be far quicker to replicate entire trees if you knew nothing in them had changed.