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The story started many years ago, when I was playing with a baremetal code ("BIOS") for ABit AB-PB4. The project has been put on a hiatus after I created a serial console which allowed me to poke memory and IO space. It was even possible to manually dump sectors from CDROM, but I lost the interest to write an API and turn the "BIOS" into a primitive OS. Years later when I've discovered the Retroweb I've returned to the idea while being equipped with modern tools.

Let's say we want to boot a linux distribution on a 486 motherboard. We hit the wall even before downloading anything. The is almost none modern distribution which is compiled for 486 architecture and if we find a 486 compatible distribution installation image we gonna quickly hit another wall: old BIOSes doesn't support boot from a CD drive. The we can set up an SD card and then we will hit the third wall: old BIOSes doesn't also support big drives and if they do (~ 8GB) LBA addressing support for them is terrible.

Coreboot just do the hardware initialization and loads payloads. The hardware initialization part set chipset's registers, detects RAM and cache size, enumerates the PCI bus and create system tables (SMBIOS, MP, ACPI, ...). Then it can choose one of the payloads and run it (e.g. one is a doom clone). The most important payload is an implementation of the IBM compatible BIOS. It is called SeaBIOS.

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