Starting this in TUHS due to UNIX relevance, but with the heavy disclaimer this should quickly diverge to COFF if it drifts into foreign waters. I've gotten to reading about 5ESS lately, and it seems there are many in use still today. I found myself wondering what the evolution has looked like as far as computing hardware and operating systems involved. DMERT ran on the 3B-20D supporting the 5ESS systems in the early 80s, at the same time that UNIX 4.x was making rounds on the 3B-20S. A 5ESS manual from 2001[1] mentions UNIX RTR (Real-Time Reliable) of the DMERT lineage. Wikipedia[2] suggests 5ESS is still very much in use and mentions more modern systems like VCDX; its "Sun Microsystems SPARC workstation runs the UNIX-based Solaris (operating system) that executes a 3B20/21D processor MERT OS emulation system." This sounds like the Lucent 3B20 emulator. Is there still a line of UNIX RTR/DMERT being maintained to this day? Or are users left with other avenues to keep their hardware updated if necessary? [1] - https://documentation.nokia.com/cgi-bin/dbaccessfilename.cgi/235600510_V1_5… [2] - https://en.wikipedia.org/wiki/5ESS_Switching_System - Matt G.