The kernel does two things:

  A) keeps track of stuff.
  B) responds to requests from programs and hardware.

Boot, enumerate/initialize hardware:
  RAM, MMU (page tables)
  Processors, Timers
  I/O devices: Console, Root
    "Early printk", /dev/console for diagnostic boot messages
    Legacy root= vs initramfs.
  /init (filesystem, executable format)
    ELF spec, muppet labs!  (man 5 elf)
    Dynamic linker actually getting loaded rather than the executable.
    binfmt misc, the old a.out.

Modules.

The root filesystem.
  mmap, page cache, faulting executables, linker (normal, PIC, flat).