[samcheng]

What about Apple's M-series chips, which have on-die RAM? Is that RAM significantly more expensive per GB due to the more expensive process?

(It's certainly exorbitantly expensive for retail consumers at $200 for an 8 GB RAM upgrade on a Macbook!)

[wmf]

Apple does not have on-die RAM. The SoC is a normal logic die and the RAM is regular DRAM.

[samcheng]

Ah - I see, the DRAM is literally BGA'd right next to the die. So that $200 upcharge is mostly profit... Thank you!

[vbezhenar]

It's called "package on package". The RAM is different chip, however it's located very close to the CPU chip and both are under a single cover. The end result is a "package".

I think that GPUs use similar approach.

[RF_Savage]

AMD Vega used HBM next to the GPU die, but most GPU manufacturers are now back to discrete chips on the GPU circuit board.