Program status word / Memory or general purpose register read-out could then be accomplished by observing and noting the console lights.
On later platforms with multiple users, this method was impractical and so single step execution had to be performed using software techniques.
In some software products which facilitate debugging of High level languages, it is possible to execute an entire HLL statement at a time.
Full Instruction set simulators however could provide instruction stepping with or without any source, since they operate at machine code level, optionally providing full trace and debugging information to whatever higher level was available through such integration.
In addition they may also optionally allow stepping through each assembly (machine) instruction generated by a HLL statement.