That machine had an instruction to execute an
instruction that was held
in a register! ...
Another set of memories from vaious 3rd gen machines ...
All three of ICT 1900, IBM 360, Honeywell Level 66 (=6000) have instructions
to obey the instruction at <memory address> which, at the time they were
designed, must have seemed a way of getting the benefits of
self-modification without the problems.
IBM's EX and ICT's OBEY both were simple (indexed) instructions - Honeywell,
of course, also did something* too clever to the target instruction.
* I forget what ... but then I only wrote two small modules in assembler for
our L66 - everything else I did on that machine was either in Fortran or B.
Andy