Where software meets hardware..

[Darren Pilgrim]

David King wrote:
>> 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?

Look up hot-carrier injection and quantum electron tunneling.  Basically 
such devices use over-voltage to cause electron migration within the 
device.  The migrated electrons result in measurable changes in the 
electrical characteristics of the gate (i.e., threshold voltage).  The 
process is reversable but destructive, since you can't put the electrons 
back exactly where they were before.  This is also why EEPROMs and flash 
devices have write-count lifetimes.

-- 
Darren Pilgrim