<Err, 'PDP11' covers a whole lot of machines from something like an SBC2 <in a BA11-V (about the size off 2 modern notebooks stacked on top of ea <other) to a PDP11/70 in a number of 6' racks. There's no 'average' <machine IMHO No to mention the PDT series and PRO350/380 series also a s100 board by marinechip systems. <There's a whole lot of OS's. Among them are : <RT11 (single user, a little like CP/M) RT-11 had four monitors, SJ/single job, FB/forground background, XM/extended memory and a BM/batch monitor. Later versions (v5.5 or so) have networking hooks for DECnet, lat and other services. I run RT-11 on a: BDV-11 (11/23A) BA11S (11/23B) BA11N (J11) PDT11/130 Mongo (a dual by 12 slot rack with 11/23A, 1mb ram, DLV11j, BDV11b rom(boot), H780 power) <RSX-11 (many varients - the forerunner of VMS in many ways) RSX-11 was the forerunner of VMS. It's realtime capable, multitasking and can support timsharing as well. DECnet was supported for either DDCMP or Eithernet networking. POS POS was a single user version of RSX-11 with a GUI interface for the PRO300 series. It supported a Phone management system, large format videodisk and DECnet via serial or Eithernet. <DOS-11 (one user at a time, single tasking?) <Tripos (Cambidge University's locally-written portable OS) <Fuzzball (An OS with TCP/IP networking, using many utilities from RT11 <TSX-11 (multi-user OS built on top of RT11) <Unix (certainly v5, v6, v7 and some BSD's ran on PDP11's) V7 was supported on the MicroPDP-11 using the J11 (has I&D space) cpu. <Xenix ? (I've heard rumours of a PDP11 port) There was also Venix (I have that on a pro350). <UCSD p-system Learned Pascal using that on an H-11 varient. <RSTS/E (never used it, so can't say what it's like) Resource sharing, timesharing looks like rsx, rt or basic depending on the monitor running. I have RSTS on DU0: of my system and RT-11 on DU1: Later versions of RSTS support DECnet networking. <XXDP+ (diagnostic OS) Realllllly slooowwww. Also CTS-300/rt-11 Commercial operating system supporting DIbol which was a sorta cobol. DSM-11 a database system with MUMPS as the language There as CAPS a cassette OS for the TU60 dectape. Micropower Pascal (host is RT) target is OS less and can be what ever the applications is. <There were also some stand-alone programs that didn't need an OS, <including an assembler and Basic from DEC (which loaded from paper tape <FIG-forth, a couple of other Forths, etc. IOX, not an OS but an IO excutive for building custom systems. Allison