I used CTSS in the 1971/72, my first year at MIT.  They gave undergrads spare
time accounts on any systems there.  It was at the end of its life, was way
overloaded, and ran on a 7094 that stuck around for quite a few years later.

It didn't have a hierarchical file system per se.  Just a single level of
directories.  I can't remember how you named an other user's directory
or even the system one.

Multics fixed that and added much more.

So, I went to see what I could find on the web...

	http://larch-www.lcs.mit.edu:8001/~corbato/turing91

is a nice read.