NFC chips come from the manufacturer in a default “blank” state as defined by the technical specifications for that NFC chip. This blank state includes the format, the initial values of the user memory and the configuration of the NFC chip features. Often NFC software requires the NFC tags to be encoded before they will work in the software.
Some NFC chip types come pre-NDEF formatted; the chip is permanently formatted as NDEF and an empty NDEF message is written into user memory. The NFC tag can subsequently be encoded with a different NDEF message, but it is not possible to change the format. The user memory beyond the empty NDEF message is all 0s.
For chip types that are not pre-NDEF formatted, the initial state of user memory is all 0s and no formatting exists. The NFC tag can then be formatted and written to during encoding.