He ejected the USB drive labeled 9.00 and tossed it into a drawer filled with old hard drives and tangled cables. He scrolled over to the new icon that had appeared on his menu bar— Homebrew Store .

A PS4 doesn't actually delete its previous firmware when it updates; it stores the current version and the immediately preceding version in two different hardware "slots" (CoreOS slots).

: Solder thin wires from your flashing hardware device directly to the tiny pins of the Syscon and Nor Flash chips.

How to Revert the PS4 to a Previous Firmware (Full Tutorial)