CHIP

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The CHIP tag is a 16-bit unsigned integer (uint16_t) that denotes the type of chip the firmware is to be installed to. It is one of the few tags that is not read from the fuses, being hardcoded in the bootchain. It is used to prevent [supposedly] incompatible firmwares from being installed. A firmware is truly incompatible if it uses instructions only available on newer processors.

Processors

Recovery Mode string

If you connect a device in Recovery Mode to your computer, there is a small section in the device's USB "serial number" that contains the CPID, among other information.