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# Applicability
This document applies to the tip-of-trunk version of the PiDP-8/I software. If you are still running the last stable release, v2017.12.22, you'll need to either [upgrade](/#updating) or switch to the [last version of this document as of the time of that stable release](/info/37b9507f98f).
# The Situation
In February 2016, Norman Davie released a program he called [Deeper Thought](https://groups.google.com/forum/#!msg/pidp-8/tbciVNoZJbw/AMjywRKLAwAJ) after an earlier program by Steve Gibson called [Deep Thought](https://www.grc.com/pdp-8/deepthought-sbc.htm). The most important difference between these two programs for our purposes here is that instead of running as PDP-8 code within the simulator, as Gibson's program does, Davie's Deeper Thought runs as a native program on the Raspberry Pi, using a version of Oscar Vermeulen's original `gpio.c` module to manipulate the LEDs on the PiDP-8/I's front panel and read its switches.
Davie's program has been [forked several times](https://github.com/timdawg/Deeper-Tought-2/network), but this mode of operation remains in all of the versions I've tried.
When Ian Schofield created the [incandescent lamp simulator](/wiki?name=Incandescent+Lamp+Simulator) (ILS) for the PiDP-8/I, he changed the external interface in a couple of ways which prevented it from being used with any of these versions of Deeper Thought.
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