LC

Understand the Reset Vector: Why CPU Starts at 0xFFFFFFF0

easy3/8

Use QEMU Monitor to Inspect BIOS Entry State Read the BIOS Memory Map: A20 Line and Reserved Regions

Language

Compiler

2.0s Limit 256MB

Implementation

Write a program that explains and demonstrates the reset vector.

Requirements:

Explain why the CPU starts at 0xFFFFFFF0 instead of 0x00000000
Show the calculation: how CS and IP form the physical address
Explain the FAR JMP instruction at the reset vector
Describe segment:offset addressing on the 8086
Show the memory layout of the 8086 (1MB address space)
Explain why real mode is still used today
Demonstrate the reset vector calculation with code
Print a clear, educational explanation

Why This Matters

0xFFFFFFF0 is documented in the Intel Software Developer's Manual Volume 3A as the architectural reset vector, and coreboot's very first assembly instruction lives at that exact offset in every x86 ROM image. This 8086-era compatibility hack is why a brand-new 64-bit Ryzen or Xeon chip still boots by pretending to be a 1978 processor for its first few instructions.

Hints

0 / 3 revealed

Validation Suite

main.c

Workspace 1.0