[calf]

This question bothers me because I have never found a clear authoritative documentation.

The more detailed sources say, contra the mainstream impression, that Apple Silicon's vaguely-named "unified memory" is technically a hybrid System-on-Chip and System-in-Package architecture. The memory banks DRAM are on a second die (one source said it is made by Samsung), but the RAM controller sits on the CPU die and manages the RAM for the unified memory pool for graphics/main/neural memory usage (hence, "unified" from an ISA perspective). Both IC dies coexists on a shared enclosed package as a single microchip. Technically this is still called a System-on-Chip architecture according to Wikipedia because the electrical engineering definition allows for some parts, such as RAM or I/O, to still exist separately off the main piece of silicon die yet still be called an SoC architecture. In short, it is not a monolithic SoC.

I have tried several times to find citations about this but it is an ambiguous point that is often glossed over, as a kind of hardware abstraction.