: Open the RetroBoot_1.2.1_Standalone.zip and drag all contents directly to the root of your USB drive.
for systems like NES, SNES, Genesis, and even some N64 and Dreamcast. Zero-Footprint retroboot 121 install
"Retroboot 121 Installation Guide: Bringing Retro Goodness to Your Device" : Open the RetroBoot_1
You might wonder why you should specifically install version 1.21 instead of the newest release (e.g., 1.23 or 1.24). Here is the breakdown: retroboot 121 install