MCU die shot (STM32F100) - what's what and why...

[TinkeringSteve]

... why is there this rusty pattern on the right?
Artifact of the chemical uncovering method, or is this flash and you can actually see written vs. unwritten bits?

I'd guess on the left is RAM top and bottom, or if the right is not flash despite those flash blocks looking grids,
maybe top is RAM and bottom flash? I'd not not why else that separation, I don't think the F100 had different RAm segments
like extra CCM or such.
The actual CPU and perhaps some peripherals are in the lower right, right?
And GPIOs and such at the outer "frame"?

https://en.wikipedia.org/wiki/STM32#/media/File:STM32F100C4T6B-HD.jpg

[Manicken]

Normally you cannot see what is what as the transistors are at the "bottom" and on top of that is the power and signal wiring, my guess is that top left is ram left bottom is flash and the "rusty" part is the peripherals and the CPU, the lower right corner can be power regulators and clock Machinery ( i.e
 the most basic stuff as that would not contain so much transistors and then there is not much wiring on top