Ivan Sutherland's Sketchpad was developed for the TX-2! Here's a paper where he describes his experience working with it: <a href="https://www.ll.mit.edu/sites/default/files/page/doc/2018-05/LookingBack_19_1.pdf" rel="nofollow">https://www.ll.mit.edu/sites/default/files/page/doc/2018-05/...</a>.<p>One interesting thing that caught my eye was this:<p>> Hardware bugs also happened, through component or engineering failure; TX-2 was, after all, an experimental computer. The quickest way to get a bug fixed was to write a very simple program that failed in spite of obvious correctness, and the easiest way to “explain” this bug to the hardware engineers was to show them a Polaroid photograph of the panel of toggle switches that “stored” 24 words of 38 bits each and the console lights. Leaving a program in toggle switch memory that should obviously work, but failed, was a sure way to get the hardware people to fix a bug.<p>I checked out a memorandum on the toggle switch storage system (<a href="http://www.bitsavers.org/pdf/mit/tx-2/6M-5661_Toggle_Switch_Storage_System_TX-2_Apr1958.pdf" rel="nofollow">http://www.bitsavers.org/pdf/mit/tx-2/6M-5661_Toggle_Switch_...</a>). From what I understand, it allowed direct manual input of data and instructions into memory through these switches. TX-2 had 24 registers, each 37 bits long. Sixteen of these could be manipulated using the toggle switches on the main control panel. So, programmers could directly alter instructions.<p>The system involved some kind of resistor-switch matrix (not sure exactly what it does though!). But it enabled switches to toggle between 0 (ground position) and 1 (connected to some kind of resistor driver) - this, in turn, would help represent individual bits. Neat stuff!<p>If anyone has fun stories related to all this, I'd love to hear them!