"Boot", as in "boot up your computer" or "reboot". Riding boots used to (and still do, AFAIK) have "bootstraps" formed into loops at the tops of the boots, for pulling the boots on. Someone who improves their lot in life with no outside help is said to have "pulled himself up by his bootstraps" -- a form of levitation, as it were. Early computers had very minimal programs stored in ROM or even entered by hand via switches (yes, I did this in the 70s) that would then load a larger program from disk or tape, which would load the operating system. These "boot" programs allowed the computer to bring itself up, with the least possible support from any other resource.