Cold Boot (S01E02) The Reset Vector

**Cold Boot S01E02 — The Reset Vector** When a CPU wakes from reset, it knows almost nothing — not about disks, keyboards, or screens, not even what it is. It knows exactly one thing: a single hardwired address where it must look for its first instruction. That address is the reset vector. This episode walks through what happens at that address and why it lives where it does: - Why x86 puts the reset vector at the top of the address space (0xFFFFFFF0) rather than the bottom - The real-mode segmentation quirk that lets a 1 MB-limited CPU reach a 4 GB address on its very first fetch - Why what's actually there is almost always a jump instruction — a signpost, not the real startup code - The chipset's role as matchmaker between the CPU's request and the flash chip that answers it - How other architectures handle the same problem: ARM at the bottom with a vector table, RISC-V wherever the designer chooses - And the detail that surprises most people — the firmware runs its first hundreds