Starting DOS using a Multiboot-compliant loader involves creating a custom loader that can switch the CPU from protected mode (set up by the Multiboot-compliant bootloader) back to real mode (required by DOS)
assembly
IO.SYS
IO.SYS is a hidden, system file that is loaded early in the boot process of DOS-based systems. It is essential for the operating system to function. This article looks at its structure and work towards reconstruction.
2 Stage Boot Loader
Described here are the working for a two-stage bootloader designed to initialize and load an operating system kernel in a flexible and modular manner
Creating s Boot Sector
Creating a boot sector from scratch requires knowledge of assembly language and how the BIOS works during the boot process.