How fast can a Pi boot? Are they suitable for embedded environments where "instant" booting is required? Are there any alternatives which run Linux with graphics which can boot faster?
The Pi has a weird boot sequence because of the Broadcom chip.
SBCs with uncomplicated boot loaders can get you to a shell prompt within one second of applying power; I imagine getting to a lightweight graphical environment in under 2 seconds is not hard. Doubtless you can reduce that a little with tweaking. That's a good deal faster than my car stereo, say.
There is bare metal code that almost immediately starts after powering the Pi on. A Pi3 and below with an absolute minimal Linux based OS could probably boot in 3-4 seconds or so. With the Pi4 that has changed and the EEPROM can take a few seconds on its own before the Pi even gets to the kernel loading phase.
