The 11/70 with Mr memory had battery backup on the MOS usually so they would have the saved memory content unless they powered off the battery backup. Sent from my android device. -----Original Message----- From: Noel Chiappa <jnc(a)mercury.lcs.mit.edu> To: tuhs(a)tuhs.org Cc: jnc(a)mercury.lcs.mit.edu Sent: Mon, 28 Mar 2016 10:18 Subject: Re: [TUHS] PDP-11/70 SPL (was: Early non-Unix filesystems?) Or perhaps it was added precisely to get rid of the window, and then someone discovered that it could be used to freeze the system, so they decided they'd better not document it? If the system had MOS memory, and you had to power cycle the machine to get it out of this state, there wouldn't be any evidence left of who did the deed (unless the system was writing extensive audit trailing to disk), so it would be a great 'system assasin' (aka vandal) tool. Noel PS: I guess this is more PDP-11ish than UNIXish - apologies for the off-topic!