The most on-brand HN thing I've read so far today.

Thank you!

The first is legacy BIOS: the BIOS will load the first 512 bytes of the boot sector, called the Master Boot Record (MBR) into memory location 0x7C00; they are then responsible for bootstrapping the rest of the system. Usually by doing the bare minimum to load a second-stage bootloader off the disc, and letting the second-stage bootloader do the rest of the work, since 512 bytes (actually only ~440) is really not very much.

The second is UEFI. The firmware will load a PE-formatted executable from a .efi-suffixed file on a FAT32 partition which has the EFI System Partition (ESP) flag set. Since this PE file can be any size, a second-stage bootloader is not generally necessary (but may be interesting for aesthetic reasons e.g. if you don't like PE).

https://developer.apple.com/support/downloads/Apple-File-Sys...

The boot process for HFS+ is more involved, because you have to actually read the HFS+ file system to locate the EFI image, since it's stored in a regular file.

I'm not sure what happens after jumping into the EFI code.

(Disclaimer: I worked on the linked document.)

TL;DR likely read only firmware, possibly more low level than a BIOS, UEFI, or Coreboot implementation would be.

Edit: then again, they could be shipping a full EFI implementation like they do on their x86 offerings.

More information: https://github.com/AsahiLinux/docs/wiki/HW%3AUSB-PD

https://www.youtube.com/watch?v=d5s9fYfvzmY

(In addition to the docs, as outlined by terramex)

This made me laugh because I spent a good chunk of last weekend trying to debug a problem with some of my old computer hardware and the problem turned out to be a link that couldn't handle anything over 150 baud.

Now we're squirting 115,200 straight out of a chip. It's like the future!

(Raises are not accepted after you've already called.)