Extracting Firmware or Bios

I don`t know where other place to ask so here`s the place.
I read in the news bout hardware hacking such as Bios and the Firmware hacking. And i'm curious just how exactly do we extract the firmware information ? I mean it`s ll embeded into a rom chip right so how the hell we extract it?

Hypothetically say I had the requisite EE knowledge, all the tools necessary... how do you get hold of the chip technical specs?  Wouldn't it be not publicly available most of the time?