Where software meets hardware..

[David King]

> The BIOS is also simply a piece of software, stored
> in a chip on the mainboard.

In memory, a program's bits are represented by the voltages of  
transistors in particular places on a DRAM chip. On a CD, by the  
width of pits in the surface of the CD. In chips like BIOS and other  
types of firmware that don't need power to maintain their state but  
that can be re-written, how are the bits physically represented, and  
how are they read out to memory?