You are obviously new to the computer field. Back in my day (he said from his rocking chair) we had to modify hardware to get things to work.<p>For example, a teletype (<a href="https://en.wikipedia.org/wiki/Teletype_Model_33" rel="nofollow">https://en.wikipedia.org/wiki/Teletype_Model_33</a>) used either current or voltage in the interface so you had to physically modify the computer motherboard (<a href="https://www.foxdata.com/blog/time-to-test-the-data-general-mv2000-dc/" rel="nofollow">https://www.foxdata.com/blog/time-to-test-the-data-general-m...</a>) with wire cutters or a soldering gun.<p>Or you had to muck about with the patch panel in your card sorter (<a href="http://www.columbia.edu/cu/computinghistory/plugboard.html" rel="nofollow">http://www.columbia.edu/cu/computinghistory/plugboard.html</a>)<p>Or you had to "reseat" (open the computer, pull out each card, and plug it back in) the cards every morning when you started the IBM Series 1 computer. (<a href="http://www.ricomputermuseum.org/Home/equipment/ibm-series1" rel="nofollow">http://www.ricomputermuseum.org/Home/equipment/ibm-series1</a>)<p>Or you had to read (by eye) your paper tape looking for a jump instruction you could hand punch (<a href="https://collection.maas.museum/object/373326" rel="nofollow">https://collection.maas.museum/object/373326</a> or one you made yourself) a "JUMP" instruction to your new "SUBROUTINE" (that you hand punched) to splice the old one out of line and hand compute the return address to skip the old routine.<p>Or hand wiring your own core memory array (<a href="http://www.ricomputermuseum.org/Home/interesting_computer_items/magnetic-core-memory" rel="nofollow">http://www.ricomputermuseum.org/Home/interesting_computer_it...</a>) since an order for 64 "bytes" of core was delivered as 512 tiny core "donuts".<p>Or physically enter the paper tape boot loader from the front panel switches
(<a href="https://raymii.org/s/articles/Toggling_in_a_simple_program_on_the_DEC_PDP-8_and_PiDP-8_using_the_switch_register.html" rel="nofollow">https://raymii.org/s/articles/Toggling_in_a_simple_program_o...</a>)<p>Or implement "Halt And Catch Fire"... The Intel chip had the "FOOF" instruction (<a href="https://en.wikipedia.org/wiki/Pentium_F00F_bug" rel="nofollow">https://en.wikipedia.org/wiki/Pentium_F00F_bug</a>) which stopped the processor cold. You had to repower the computer to reboot. Also, your CRT display needed the correct settings for things like "horizontal, vertical, frontporch, backporch", etc. If they were wrong your display could physically catch fire. SO... you created a program to set the fire-causing display settings and then execute a FOOF instruction... The computer stopped and the display caught fire.