Harold Hallikainen wrote:
> The PDP-8 was an interesting machine. It did not have a stack. When you
> did a subroutine call, the return address was put in the first location
> in the subroutine. Execution would start at the next address.

That was quite common for machines of that era.  Most of the contemporaries
of the PDP-8 worked the same way, such as the DG Nova, the Varian 620, a
small Honeywell I forget the name of, etc.  Hardware stacks became popular
in minicomputers (microcontrollers in rack mount boxes for you young-uns)
only later.

Note that even the IBM 360 architecture wasn't really based on a hardware
stack.  The common subroutine call instruction was BALR (branch and link
register).  The return address was stuffed in a register.  At least that
allowed recursion if the register was handled correctly.


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