Volatile storage devices (i.e. RAM) shall serve exclusively as read/write cache for non-volatile storage devices. From the perspective of all software except for the operating system, the machine must present a single address space which can be considered non-volatile. No computer system obeys this law which takes longer to fully recover its state from a disruption of its power source than an electric lamp would.
Personal computer operating systems known to obey this law:
Notes and observations:
When you make a deliberate change to the system, the change stays made: this is the basic reliability we expect of paper and pencil. And of almost every other tool, save for our computers!
To be continued.
[*] Corrections are welcome.