difference between microsim and orcad pspice

The same thing. Orcad bought the microsim and combine with their software. If you plan to use try to use Orcad instead of microsim.

The microsim pspice had their own simplified schematic capture for making the net list. When orcad took over, they had their more complex schematic capture be the generator of the netlist. People complained and the had the option of using either capture loaded on your computer when you installed the program.

If I remember right, microsim used a hardware key.