From mboxrd@z Thu Jan 1 00:00:00 1970 From: jnc@mercury.lcs.mit.edu (Noel Chiappa) Date: Wed, 25 Apr 2018 18:46:46 -0400 (EDT) Subject: [TUHS] /dev/drum Message-ID: <20180425224646.80DB718C086@mercury.lcs.mit.edu> > From: Johnny Billquist > I don't know exactly why DEC left the last three tracks unused. Might > have been for diagnostic tools to have a scratch area to play with. > Might have been that those tracks were found to be less reliable. Or > maybe something completely different. But it was not for bad block > replacement, as DEC didn't even do that on RK05 The "pdp11 peripherals handbook" (1975 edition at least, I can't be bothered to check them all) says, for the RK11: "Tracks/surface: 200+3 spare" and for the RP11: "Tracks/surface: 400 (plus 6 spares)" which sounds like it could be for bad block replacement, but the RP11-C Maintenance Manual says (pg. 3-10) "the inner-most cylinders 400-405 are only used for maintenance". Unix blithely ignored all that, and used every block available on both the RK11 and RP11. Noel