Just to add to what John wrote, a VERY quick search of RT-11 source code starting with V05.00 of RT-11 does not encounter the MRRT$ conditional. As for V04.00 of RT-11, the conditional does appear in RMONSJ.MAC, but not in RMONFB.MAC, so it seems as if the MRRT$ Memory Resident aspect of RT-11 was available only with the SJ Monitor. A quick search of files prior to V04.00 and after produced no hits on the MRRT$ conditional symbol, so there is a possibility (very strong starting with V05.00 of RT-11) that DEC had support for MRRT-11 only with V04 of RT-11 from about 1979 to 1983. It is VERY possible that the user was responsible for producing MRRT-11 and integrating such a system. From looking at the *.Mac files for V04.00 of RT-11, the MRRT$ conditional appears in at least the RMONSJ, USR and the BSTRAP files. There is some indication that the memory resident code did not support a file system, but that is not certain. More important would be to locate the documentation for MRRT-11 to determine additional details of how it was put together and how it operated Since I have never actively used MRRT-11, I can't provide and more help at this point. Jerome Fine