9. Device tree
The device tree is a Linux kernel defined data structure that serves to inform the kernel how the hardware is setup.
Device trees serve to reduce the need for hardware vendors to patch the kernel: they just provide a device tree file instead, which is much simpler.
x86 does not use it device trees, but many other archs to, notably ARM.
This is notably because ARM boards:
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typically don’t have discoverable hardware extensions like PCI, but rather just put everything on an SoC with magic register addresses
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are made by a wide variety of vendors due to ARM’s licensing business model, which increases variability
The Linux kernel itself has several device trees under ./arch/<arch>/boot/dts, see also: https://stackoverflow.com/questions/21670967/how-to-compile-dts-linux-device-tree-source-files-to-dtb/42839737#42839737