[edsac_xyzw]

In the case of SpaceX, it seems that they use embedded Linux and C++ with x86 processors, same as standard PC processors. A reason for using embedded linux is that, it allows using standard C++ or even scripting languages for controlling the hardware from the user-space by just reading and writing files. Linux device drivers (aka kernel modules) maps the hardware to special files on /sys or /dev. For instance, it makes possible to control a GPIO (General Purpose IO) which the device driver maps to sysfs special file system, by just writing 1 or 0 to the file a like /sys/class/gpio/gpio4/value which would enable GPIO 4 and turn on a LED attached to it. Another practical example about this feature is that, on Linux, it is possible to turn on or turn off the keyboard capslock LED by writing to some /sys/class/leds file such as "$ echo 1 > /sys/class/leds/input7\:\:capslock/brightness" which turns on the Capslock LED. By writing 0 to it, the LED is turned off.

This feature of Unix and Linux allows controlling the hardware with any programming language capable of reading and writing files, including Python and standard C++. I guess that they may be using standard PC hardware with industrial IO card. They may also use a single-board computer or custom board with x86 low-power variants processors built for embedded applications as SOC system-on-chip. One example of low power x86-SOC based processor is: https://www.cnx-software.com/2015/04/09/vortex86dx3-is-a-new...