This is a guest post by Ricardo "arcee" Cerqueira who takes things apart for sport, on a quest to understand how they work. He currently works on Android devices at Cyanogen.

As people started receiving their Nexus 6Ps, some began freaking out over a new message that comes up on the screen when booting into fastboot mode: “QFUSE: ENABLED,” with wild speculative theories coming up regarding what it does and doesn’t do, what kind of limitations it’s imposing, and wondering if and how it can be “disabled.” So... what’s this qFuse thing, anyway?

Think of an eFuse as the mind’s eye representation of a bit that only flips one way, or something that can only be done once on a piece of writeable flash.

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