In the case it was the custom-designed system-on-a-chip, Apple A4.
It’s always a nightmare when Apple’s Official Tools start showing error.
Moreover, instead of matching competing display sizes of the time, they leap-frogged over them.
To boost pixel count yet maintain compatibility with existing apps, Apple doubled both horizontal and vertical counts, while keeping the physical size constant at 3.5-inches. That brought the density up from 163ppi to 326ppi, and Apple made the argument that, at that point, the pixels disappeared. The cellular radio stayed pretty much the same, at least at first, though Apple did switch from mini to micro SIM for the carrier card. The Wi-Fi radio went to 802.11 g/b/n, though only on the 2.4Mhz band.
If you see an error message while trying to update your device wirelessly, learn what to do.