grub's internals: how does stage1 find stage2?

[Paul Bolle]

I'm just curious about the way stage1 finds the location of stage2. It
seems that grub stores this information in 0x42-43, 0x44-47 and/or
0x48-49. I had a look at a couple of MBR's installed by grub, but I
couldn't figure out how the values found at (one of) those places in the
MBR tell stage1 where to look for stage2.

Of course I did have a look at the Texinfo manual and the source of grub
but that didn't help me much (it doesn't help that I know nothing about
assembler so it's hard for me to understand stage1.S).

Does anyone know where this process (stage1 finding stage2) is explained
in more detail?