runs the boot script you’ve selected either with the IF switches or by
passing it on the command line to `pidp8i-sim` or `pdp8`.  This brings
the simulator up in a known state, with no persistence between restarts
other than what was written to the simulated storage devices before the
last shutdown.

On a real PDP-8 with core memory, however, the values in memory will
persist for weeks without power and they aren’t zeroed on power-up.

Since the CPU doesn’t start executing anything on power-up in a stock
PDP-8 configuration, this means the user can toggle in a program/OS
restart address with the switch register (SR), load it into the program
counter (PC) with the Load Addr switch, then START the CPU to restart
their program without having to reload it from tape or disk.

There were also several power fail and restart options designed and made
available for the PDP-8 series throughout its lifetime. One of these,
the KP8-I for the PDP-8/I would detect a power fail condition, then in
the brief time window while the power supply’s reservoir capacitors kept
the computer running, this option card would raise an interrupt, giving
a user-written routine up to 1 millisecond to save important registers

runs the boot script you’ve selected either with the IF switches or by
passing it on the command line to `pidp8i-sim` or `pdp8`.  This brings
the simulator up in a known state, with no persistence between restarts
other than what was written to the simulated storage devices before the
last shutdown.

On a real PDP-8 with core memory, however, the values in memory will
persist for weeks without power; core memory on a PDP-8 is not zeroed on
power-up, unlike RAM on a modern computer.  Since the CPU doesn’t start
executing anything on power-up in a stock PDP-8 configuration, this
means the user can toggle in a program/OS restart address with the
switch register (SR), load it into the program counter (PC) with the
Load Addr switch, then START the CPU to restart their program without
having to reload it from tape or disk.

There were also several power fail and restart options designed and made
available for the PDP-8 series throughout its lifetime. One of these,
the KP8-I for the PDP-8/I would detect a power fail condition, then in
the brief time window while the power supply’s reservoir capacitors kept
the computer running, this option card would raise an interrupt, giving
a user-written routine up to 1 millisecond to save important registers