Single Directory Disks Some of us old timers will perhaps remember single directory Files-11 devices. These were invented (I believe) for the old TU56 DECtapes...the ones that could fall off the reel, get rewound covered with dust, be replaced, and still read all data.... On disks, under RSX, setting DV_SDI in the UCB characteristics caused a file access to ignore the directory part of the access, and use filename only (using [000,000]) for the directory part). This was actually useful with things like memory disks, RT emulation, and so on. It seems that in VMS, there's almost no residue of this behavior left. If you set the dev$m_sdi bit in ucb$l_devchar, things work basically normally. There are two exceptions: 1. Directory listings stop after one directory (due to the details of how RM0SCAN.MAR is coded), and 2. RMS does not try to read directories with read-logical and cache them, but instead gets the ACP or XQP to read the directory. This slows things down a little, causes MONITOR FCP to show more XQP activity, and allows anything that wants to affect the XQP operation to in principle affect directory operations also. VMS Backup operation seems to be unaffected by the bit. There is code that could cause problems in other parts of RMS, but it seems to be bypassed presently because the code tests to see if it's on a disk first, then skips around the single directory test if so. The assumption appears to be that the only single directory device is magtape. I think this is a good change - nobody much used single directory disks in RSX anyhow - but one that is in the "interesting arcana" category that should be shared... Glenn Everhart@raxco.com