Some applications might have used it (the story about the KS11 bug with the KW11-A confirms they did use it on that machine), but I found no trace of use of it in a quick scan of the entire Version 1 source (the one which is extant). Also, the first file in the OS source: https://www.tuhs.org/cgi-bin/utree.pl?file=V1/u0.s lists the addresses of all device registers, and the KE11-A isn't there. If the KE11 is needed to run some application on the -11/04, there are KE11-B's (program compatible, but a single hex card) available, ISTR. For emulation, something (SIMH?) supports it, since the TV -11 on ITS (now running in emulation,I'm pretty sure) uses it. Noel