Thu Nov 08, 2012 6:43 pm
A PI doesn't have a BIOS, a program that is always available, (in ROM) and starts up many of the hardware features of the computer, including the video system, it also provides the shapes for letters, so it can put readable text on the screen, and a configuration menu, and lastly it boots more software from the harddisk (or floppy, or CD, and sometimes from a network).
The PI doesn't have all this, it only has a very-very small program that can do just one thing, and that is that it reads a slightly bigger program from a SD-card, that program does the things that a normal BIOS does, (and more).
So without an SD-card nothing at all happens.