It serves the network protocol 9P and runs as a user space daemon, like most Plan 9 file servers.
[1] Important features include: To access a snapshot, one would connect to a running fossil instance (“mount” it) and change directory to the desired snapshot, e.g. /snapshot/yyyy/mmdd/hhmm (with yyyy, mm, dd, hh, mm meaning year, month, day, hour, minute).
To access an archive (permanent snapshot), a directory of the form /archive/yyyy/mmdds (with yyyy, mm, dd, s meaning year, month, day, sequence number) would be used.
Fossil was designed and implemented by Sean Quinlan, Jim McKie and Russ Cox at Bell Labs and added to the Plan 9 distribution at the end of 2002.
The permanent storage for fossil is provided by Venti, which typically stores data on hard drives, which have much lower access times than optical discs.